Big Brother Instinct: When Luke gets warped half-way around the world, Asch immediately sets off to find him. The distance between Kimlasca-Lavender and Malkuth is a few days by coach. Asch meets up with him at Cheagle Woods in two.
Breakout Character: Cantabile didn't actually appear in the game, and was only mentioned in Tales of Fandom.
Cruel Mercy: Sync's final encounter is this. Even when left with a dagger, he couldn't bring himself to commit suicide.
Enemy Mine: Guy gets kidnapped by Cantabile and the group goes after him. Where do they find him? Drinking tea with her in a cafe, having a civil discussion. To be fair at this point Guy wasn't aware of the extent of Cantabile's plans and was simply happy to see her alive. However, considering Guy's loyalties were already in question at this point, it's needless to say that the group is a tad miffed.
Foregone Conclusion: Though Asch's presence changes many of the events in the story, several major events were required to happen in order to keep the plot moving along, such as Luke destroying Akzeriuth.
For Want of a Nail: Essentially what would happen if Luke reunited with his family... after they mistake his replica for him.
Asch as well, After Luke beats him in a duel, and is chosen to go to the Tower of Rem instead of Asch.
Heroes Want Redheads: Well, Tear and Natalia certainly do. Noelle also comments on Luke's attractiveness.
Heroic Sacrifice: Asch and Luke fight each other over who get's to make one at the tower also Luke has apparently made another one as of Chapter 81
Identical Twin ID Tag: Since Luke skips his Important Haircut in this story, the only way the party, or anybody for that matter, can differentiate Asch and Luke are their clothes. Played with when the two use this to their advantage to switch places without anybody being the wiser except Jade, of course.
Playing this more straight, Asch has a scar that's hidden by his hair that he got trying to escape from Choral Castle. Luke has no such scar. This is how the villains can tell them apart.
Leaning on the Fourth Wall: The characters make several comments throughout the story that poke fun at various aspects of the game it's based on, such as Luke commenting that he hates Daath, since nothing good ever happens there, and Asch commenting that had he joined Van, he'd probably have done something stupid like joined the Oracle Knights.
My God, What Have I Done?: Natalia, after trying to turn Luke over to the God Generals, and she finds out that not only were the God Generals not going to keep their word of returning him to Batical, but that it was actually Asch, who had switched with Luke.
Plot Detour: Averted. In the original game, the gang has to pass through Fubras River since the bridge to Akzeriuth was down. There was no such problems here and they got to see what the town had to offer before the subsequent miasma outbreak and destruction.
Spanner in the Works: The story is based on Luke become on to Van: convincing Asch to stay with his family instead of joining Van. This leads to Van showing a much greater degree of open contempt for Luke, since he serves as the primary anchor for Asch. It also makes Luke a much bigger target, since Van knows that if he dies, he can blame it on the score and have Asch join him.
Token Evil Teammate: At first, Asch shows a mutual annoyance to everyone but Luke, and he holds contempt especially towards Tear and Guy.
Twin Switch: Apparently, this is Luke and Asch's favorite game.
Twin Telepathy: Asch and Luke learn how to use it seamlessly shortly after returning to Batical for the first time. They don't reveal it to the rest of the party until much later, leaving them baffled as to how the hell they seem to get into fights or make up without even speaking to one another. They also use it to greater effect against Van, coordinating their attacks to create an opening.