Here is every scene in the game in which Sync appears, or is mentioned in a non-opinionated way, excluding skits. Script reference from Souya's site.
The party runs off. Four God-Generals can be seen at the entrance...
Legretta: Have you found Fon Master Ion?Dist floats in...
Dist: Ahh hah hah hah hah! That's why I told you!
Sync: Withdraw the troops from Engeve and St. Binah.
Largo: But...!
Sync: Your wound still hasn't healed. The Necromancer almost killed you. Why don't you take a break? And besides, the only way for them to cross the border is through Kaitzur. If we stay here and antagonize the Malkuth military, it could spark a diplomatic incident.
Dist: Hey! Stop ignoring me!
Legretta: So next comes deciding how to deal with them at Kaitzur. Let's return to the Tartarus for now and consider matters there.
Largo: Inform the troops! First Division, withdraw!
Soldier: Yes, sir!
The soldier runs off. The God-Generals depart, leaving Dist alone.
Back in the room with the strange machine.
Dist: ...Ah, I see. Even the fonon frequency is the same. This is a perfect creation.
Sync: I see no reason to answer that question.
Guy comes running in and tries to hit Sync, who dodges.
Sync: No!Guy gets a hold of a disc, then goes after Sync again. Sync's mask comes off.
Guy: ...What? ...You?Sync hits Guy and grabs his mask before anyone else sees his face.
Sync: Damn it, they're here!
Sync comes running.
Tear: (!)Sync attacks Guy as he runs by, then stops and turns around.
Sync: Hand those over!The party runs away. Sync gives chase.
Sync: You're not getting away!The party runs to the port.
Soldier: Master Luke, departure preparations are complete.Luke comes running with Mieu and barely makes it before the ship leaves.
Sync: ...Ow! They got away.
Dist: Ahhh hah hah hah hah! Looks like you blew this one, Sync!
Sync: Oh, it's you.
Dist: Leave the rest to me! With my ultra super hyper high-grade fonic technology, I'll flay that conniving, long-haired, four-eyed--
Sync is gone and crows can be heard cawing.
Dist: Stop! Stop! Come back! I'm not done talking!
Dist: Now, who do you think you are? Just you wait! I'm putting this down in my revenge journal!
Sync calls out from a distance.
Sync: Asch! Ion takes priority right now!
Asch: (to Sync) I know!
Asch: (to Luke, softly) Aren't you the ladies' man?
Asch and Sync swiftly climb the Tartarus and leave with Ion. Luke is still in shock over what he'd just seen.
The party goes further in and finds Largo, Sync, Asch and Ion.
Largo: The Fon Master is in the middle of a ritual. We'll have no interference from you.
Sync: Sync the Tempest, God-General of the Oracle Knights, shows no mercy.
Largo: Neither does Largo the Black Lion. Prepare!
A battle ensues with Largo and Sync.
Sync: You're a nuisance, running around like rats!The battle ends, the party wins of course.
Sync: Aah...Asch comes at Luke. The two clash, and both use the same move.
Luke: That was... That was one of Master Van's moves! How did YOU know it?!
Sync: Asch! Stop! You get carried away when left on your own. Put away your sword. Now!
Asch sheathes his sword.
Sync: Let's make a deal. In exchange for ending the fight here, we'll let the Fon Master go.
Sync: Don't forget that we're standing beneath the desert. We can bury you along with us.
Largo: We'd die, too, of course, but that is a sacrifice we're willing to make.
Tear: Luke, let's agree to their offer. Right now, we need to recover Ion and hurry to Akzeriuth.
Jade: We're already late from traveling by land.
Luke: ...All right.
Ion is released.
Anise: Ion! I was worried about you.The party goes to depart, but Guy takes one last look at the God-Generals.
Guy: ...They really are the same.Natalia and Guy leave.
Largo: (!)Natalia and Luke depart.
Sync: That's Princess Natalia? It must be fate, Largo.
Sync: There's no need for the Six God-Generals to know each other's past. You should be painfully aware of that. You, of all people--the leftover ashes of the "holy flame".
Asch: ...Tch.
Sync: That one, Guy...he knows.
The scene fades to outside, where Sync can be seen. Guy then falls to his knees, a weird symbol appearing on his arm. He's being controlled by Sync.
Luke: Guy?!
Guy knocks Luke back.
Luke: Oww! Guy, don't tell me Asch is controlling you, now?All but Ion leave.
Ion: Only a Fon Master can use Daathic fonic artes...He must be...Outside...
Sync: He's resisting more than I expected. ...No matter. They'll be caught up in Akzeriuth, anyway.
Legretta: ...Asch seems to suspect something.
Van: Asch is still a bit...dainty. He'll cause trouble if he learns that the people of the Outer Lands will be annihilated.
Legretta: Shall we have Sync keep tabs on him?
Van: Yes.
Guy tries to attack Luke all of a sudden.
Luke: Guy?Guy continues to try and attack Luke.
Largo: Don't forget about me!Natalia shoots at Largo with an arrow.
Natalia: Oh, no you don't!Guy continues to attack Luke, disarming him. The ground starts to shake.
Anise: Aah! Another earthquake!Natalia shoots an arrow into a tree, and Sync falls out.
Sync: ...The earthquake gave me away.
Luke: Are you after Ion or something else?!
Anise: Who's ordering you? Grand Maestro Mohs? The Commandant?
Largo: Either way, it's the same. We need Fon Master Ion.
Sync: We thought he'd perished along with Akzeriuth, but I guess he's tougher than the town.
Natalia: How dare you speak so shamelessly! You destroyed an entire city!
Sync: Don't accuse us. The one who destroyed Akzeriuth was that replica there.
Soldier: What's going on here?!
Sync: Largo, we're retreating for now!
Largo: I guess we have no choice...
Largo and Sync escape. Two Malkuth soldiers arrive.
The party goes to the chamber Anise's parents have.
Oliver: Anise! We heard you've been working hard at the job Ion's given you. We're so proud.
Oliver: Sync headed to the Radiation Gate.
Pamela: We heard that Arietta will be returning from the Absorption Gate.
Luke: Oh, hey, then the place is empty right now.
Tear: Let's go get Ion while that's still the case.
Natalia: Yes.
Jade: Where is Fon Master Ion?
Pamela: He was in the library, but he should be returning to his room about now.
The party exits to the deck, but there is no glyph.
Anise: Hey... the fonic glyph Iemon talked about isn't here.Sync can be seen at the other end of the deck.
Luke: So you were the intruder...Battle ensues with Sync.
Sync: I'll make the Tartarus your grave!The party wins and Sync's mask falls off.
Luke: H-hey!
Anise: It can't be... There are two Ions?!
Sync: ...Grr.
Ion: Just as I thought... You are also a replica of the Fon Master.
Guy: Wait! What do you mean "also"?!
Ion: ...I am Fon Master Ion's seventh replica-the final one.
Anise, Guy & Luke: (!)
Luke: You're a replica?!
Anise: No way... Ion...
Ion: I'm sorry Anise. It's only been about 2 years since I was born.
Anise: Two years... That's when I became one of your Guardians… Wait... was Arietta reassigned because you had no memories of the past?
Ion: Yes. The original Ion was sick. Near death. But there was no successor, so Mohs and Van used fomicry.
Sync: ...You had the closest abilities to the original. Unlike us trash.
Ion: Don't call yourself that...
Sync: That's what I am. My powers were weak, so I was cast alive into the mouth of the Mt. Zaleho volcano. A replica that can't serve as a replacement is nothing more than garbage...
Luke: ...Don't say that! We may be replicas, but we're still living beings!
Sync: I'm not interested in the naive babbling of a replica who has people who need him.
Ion: Don't talk like that! Escape from here with us! You and I are the same!
Ion walks towards Sync and extends his hand, but Sync slaps it away.
Sync: No, we're not.Sync steps backwards towards an opening on the deck.
Sync: I'm only alive so Van can use me. In the end, only those of us who are useful are kept alive out of pity…
Sync falls over the side.
Luke: I suppose if we snuck off now to ask around, Natalia would be pretty mad, huh?
Tear: ...Luke, wait! Something's odd here.
Sync: All who desire a reading of the Score, follow me! All who come shall have a reading!
Guy: Looks like our lie has become the truth.
The rest of the party heads towards the crowd.
Anise: Hold it right there! The Order of Lorelei has called a halt to all Score readings! That Scorer is a fake!
Sync: If you know that much, shouldn't you be looking for the Jewel a little harder?
Luke: You all haven't found it yet, either.
Sync: If no one finds it, we keep the upper hand.
Natalia: Brazen as ever, I see!
Anise: ...Sync, what's this New Order of Lorelei? What do you mean by Fon Master Mohs?
Sync: Didn't Mohs tell you, our darling little traitor?
Anise: ...I wasn't working for him because I wanted to!
Sync: Easy. I'm not carrying that deadweight Mohs around for kicks, either. Now, as I was saying before that interruption, all who want Score readings, follow me.
Anise: Stop right there!
NPC: We want to know the Score!
NPC 2: Yeah! He's right!
Anise: But...
Sync (in Ion's voice): Anise. Please let me go. You, of all people, should understand.
Anise: ...Ion...
Sync: Ah hah hah! Don't forget. Fighting with me means fighting with Ion.
Sync departs with part of the crowd.
The ground shakes and the Frings replica enters.
Frings: No! Mohs has moved ahead with his plan without us!The scene shifts to a view of the sea, from which something is rising. The scene cuts to Mohs, Sync, Legretta, Dist, and Largo in another location.
Mohs: ...Heh heh heh. This continent of Van's will become my new stronghold. Behold the dawn of the New Order of Lorelei! All hands, begin preparations! Heh heh heh! Hah hah hah hah!
Mohs: I shall bring prosperity to all of Auldrant in fulfillment of the Score! Hah hah hah hah!
The scene fades back to the Isle of Feres.
On Eldrant...
Mohs: Hah hah hah! Wh-what's...happening?! Sommething...innside mee..Hah hah...
Sync: Van is a Seventh Fonist. He won't see consequences like these.
Mohs: Wh...whhat are yyou...talkk...*cough*...?!
Largo: ...Pitiful. To think that he'd be so fixated upon the Score as to assume such a form...
Legretta: It's time. Let's go.
The God-Generals leave the area. The scene fades back to Grand Chokmah, where Luke and co. head to the audience chamber.
Natalia: ...One of the Oracle Knights is waiting for us up ahead.
Anise: Legretta, Largo or Sync...
Jade: Or possibly all of them.
Natalia: Largo... I...
Luke: Natalia...are you okay?
Guy: You look pale... Don't push yourself.
Natalia: I'm sorry. I'm ashamed of myself for becoming so distraught.
...But I'm all right. Let's go.
The party arrives to where they fought Van. Mohs, Legretta, Sync, and another Ion replica are there.
Anise: Ion?!
Luke looks back and sees Asch and Largo.
Asch: Replica! Why have you come here?!Asch and Largo clash weapons.
Asch: Ugh!A glow is seen and the whole place shakes.
Van: ...I'm finally able to maintain a physical form again.A light appears, fades, and reveals Van.
Mohs: Ah! Van! I'll forgive you for all your insubordination. Now, hah hah hah! Give me the Seventh Fonstone!Mohs takes it.
Mohs: Noww, noww, I can ffinally learn the sScore of the Seventh
Fonstone... Hah hah hah hah hah!!
Mohs hands the fragment to the Ion replica. Mohs, Sync, and the other Ion replica leave together.
Luke holds the Jewel up to a column of light. Everything goes white.
Luke: Uah?!Luke sees Van float by.
Luke: I see...So Master Van took Lorelei inside himself here...Then he can see Van holding a limp Sync.
Van: I will give you some of Lorelei's power. Live for a while longer and lend me your aid.
Sync: ...I didn't expect to see you here, Commandant...
Luke: ...What's going on? How come I'm seeing this?
Luke: ...Am I merging with the Planet Storm because I've started to disappear? Then, is this the planet's memory?
Asch is shown, with a sword drawn against Sync.
Luke: Is this reality?
Sync: Van hasn't yet fully recovered. And you have the Key. It may lack the Jewel, but it's still a threat. Hand it over.
Luke: Asch!
Asch: Replica! What do you want?!
Luke: I'll take the Jewel and join you! We'll set Lorelei free! Just hold out until I get there!
Asch: Don't tell me what to do!
Everything then goes white and Asch and Sync are gone.
Tear: Luke! Are you okay?The scene then fades back to the glyph.
Natalia: Luke, hang on!The scene switches back to the first room. Asch and Sync are there.
Anise: Sync!
Tear and Jade move to attack Sync, but he jumps away and disappears.
The party exits the Gate and sees Mohs, Legretta, Sync, and Van with Ion.
Ion Replica: "...Thus shall Auldrant be destroyed by the miasma and turned to dust."The Ion Replica falls to his knees.
Mohs: Hah hah hah hah hah hah! Lies! Vaaan! Izzz this ffragment really ffrom the Seventh Fonstone?!Van walks towards Luke. Luke blocks him with his hand.
Van: ...The Jewel of Lorelei?! Ugh...no! Lorelei is...awakening!The ground shakes.
Van: Uaaaaaaaaaagh!Sync whistles, and a flock of monsters come flying in.
Van: Step across the sea of corpses and make your way to me....Asch...and Luke. And at that time, I shall ask you once more.Van and the God-Generals fly away with aid of some monsters.
A weird glyph appears on the ground under the party.
Jade: Look out! It's a trap!All of a sudden, a glowing column of light appears and the glyph disappears. Luke glows for a moment.
Luke: ...Wh-what happened?The party looks up to see Sync standing at the top of the stairs.
Anise: Sync!
Sync: Even with Yulia's divine protection, power like that could harm Van.
Sync: You have two choices. Hand over the Key and join Van, or die.
Luke: ...I choose neither!
Luke: I'm freeing Lorelei. And to do that, I will defeat Master Van...and you.
Anise: Sync, you're a replica, just like Ion! Why are you helping a project like this?
Sync: I'm not like him. You know that. Ion...the seventh Ion was a naive child. He believed the Score was merely one possible choice for the future. But in the end, he couldn't oppose the Score. Fon Master Ion will die. That was the planet's memory. Your Ion died like a dog.
Anise: Take that back. Now!
Sync: No. It's the truth. But Van's plan will destroy Lorelei itself, and with it the Seventh Fonon. The Score will truly vanish.
Guy: Do you really hate the Score that much?
Sync: I was born because the Score dictated that Fon Master Ion would die. You already know that I was thrown away once.
Luke: That's why you hate the Score? Because you were thrown away?
Sync: Because I was born! I'm not even a substitute like you. I was born a piece of meat. If the Score hadn't existed, I wouldn't have been stuck with this pathetic life!
Anise: ...Are you saying you've gained nothing since you were born?
Sync: Not a thing. I'm empty. But it doesn't matter. I didn't care who it was, as long as they would erase the Score--the Seventh Fonon!
The party runs up to Sync. He jumps back.
Sync: I may be inferior, but my power of the Seventh Fonon is that of the Fon Master.Sync puts his hands together. The ground starts to shake.
Sync: You would know if I unleashed my full power! Let's test it. You, or the empty me. Let's see which side this world wants to survive!Battle.
Sync: So, how is it fighting someone who looks just like Ion?Sync is defeated.
Sync: ...Van...Destroy...Lorelei...
Sync fades away.