Crack Ship: Merkava/Vatista is oddly popular despite their interactions in their arcade ladders being less than friendly.
Complacent Gaming Syndrome: A LOT of people have been using Phonon nowadays ever since the release of Exe: Late[st]. Earlier versions of Exe: Late involved the trinity of Gordeau, Waldstein and Merkava.
Ensemble Darkhorse: With how much fan-art Vatista gets, you'd swear she's far more relevant to the plot than she actually is. In general, she's loved for having a cutedesign along with having one of the most unique movesets in the game. note She has charged attacks for every possible directional input.
Not to be outdone, Merkava is also quite popular.
The game as a whole is this for Arc System Works. Despite getting considerably less publicity than the likes of BlazBlue or Guilty Gear, Under Night In-Birth still enjoys very positive critical reception and an active and dedicated fanbase that would love for Arc and French Beard to give it more love, with plenty wondering why Exe: Late[st] hasn't been ported yet, until 2017. Then comes the question whether it will be brought to West or not. It's status as a darkhorse made it surprising that it was chosen to be part of a massive fighting game crossover alongside BlazBlue, Persona 4: Arena and RWBY.
Fanon: While the late arrival of a story mode leaves many questions about the world and the cast unanswered, Hyde is commonly portrayed as a Supreme Chef that's frequently shown serving food to the other characters.
Fan-Preferred Couple: Even though Hyde is heavily promoted as being in a tag team with Linne, alot of fans are far more interested in his relationship with Vatista instead, romantic or otherwise. It helps that most of the scenes involving Hyde and Vatista together are either hilarious, sweet, or both.
The Scrappy: Nanase is commonly hated for being an Ungrateful Bastard towards Hyde, while looking and acting like a stereotypical Tsundere in a game otherwise clean of anime cliches. People also tend to find her voice annoying.
Gordeau, due to reaching damn near Game Breaker status via the reach on his attacks. He gets nerfed in Late[st].
Chaos is often on the low-end of the spectrum, due to how little he has in the way of reversals and being unable to command Azhi Dahaka while under pressure himself.
Waldstein is a Grappler character that is generally held to be the second-best character in the game. You Can Panic Now.
Merkava is usually part of the trinity of the best characters in the game, alongside Gordeau and Waldstein, but his darkhorse status protects him from fan backlash a bit.
Akatsuki, due to his hindered physical range on his normals which prevent him from playing a decent footsies game compared to everyone else. This was before most of his buffs in Exe: Late[st].
The above examples have been mostly mitigated in Late[st], due to greatly buffing and improving most of the cast.
Phonon, ever since Exe: Late[st], where she's used very frequently due to her long range and solid hit-confirms, and is also stated to have the range of Gordeau and the combo potential of Eltnum.
Vanilla Protagonist: While Hyde is well-liked by the fanbase forhisquirks, Linne, the other protagonist, isn't nearly as popular with the crowd, since many find her personality lacking. While she's not hated, she's often forgotten about in favor of the more colorful cast that's supposed to play second-fiddle to her.