These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: Blaze Union
Anti-Climax Boss: Soltier: In A route, mostly because that route gives you the three characters best at handling him.
Not-So-Harmless Villain: ...And he's a major pain in the ass to fight in route C, where Gulcasa, Nessiah, and Baldus aren't at your disposal and thus you have to deal with all those status ailments on your own.
"Funny Aneurysm" Moment: Siskier is terrified of heights and spends the first battlefield in Chapter 2 trying not to panic when traversing the wooden-bridge mountain path to Flarewerk, to the great amusement of all. In one route, she dies jumping from a high place.
Game Breaker: The Vise card, which helps in battles even if it isn't used optimally, but basically exists to exploit Garlot's most broken battle effect (Flash Attacks do double to triple the usual damage). Gulcasa is one; Emilia also is, but you don't want to overuse her.
Eimi alone will cute your face right off. Luciana, Aegina, Eater, and Nessiah are also ridiculously adorable, and there's a reason why people have taken to miswriting Garlot's Catch Phrase (燃え上がってみせるぜ！) with the wrong kanji for "moe".
Leaked screenshots seem to suggest that instead of just giving her the prophecy and going on his merry way, Nessiah actually spends some time traveling with Eimi. Prepare for death by cute.
Given how badly Nessiah has been nerfed and the fact that he doesn't even use Reincarnation the first time you have to fight him, why does he still rate as one of the most difficult bosses of the game? Superior tactics, incessant status effects (when most of your party has low GEN and can't avoid them!), Item Break, and blanketing the screen in mooks.