Under Night In-Birth is a dojin-like fighting game series created by Ecole and French Bread, and assisted by the advises from Arc System Works' Team BlazBlue. It act as a spiritual successor of French Bread's developed fighting game series licensed by Type-Moon, Melty Blood, which eventually includes one of Melty Blood's protagonists Sion Eltnam Atlasia (dubbed as Eltnum) made her guest appearance, along with the titular protagonist of Subtle Style's dojin fighting game series Akatsuki Blitzkampf, and leading Arc System Works publishes the latest update of Melty Blood sequel Actress Again Current Code on Steam.
Behind the creation of this series was that French Bread were originally want to remake Melty Blood to HD, but eventually be stalled when Type-Moon is too busy developing Mahoutsukai no Yoru, yet instead can still give French Bread, the character Sion character as Under Night In-Birth's licensed guest fighter.
French Bread eventually continue to use the current tips which Team BlazBlue advised to developed a Dengeki Bunko and Sega licensed crossover fighting game series titled Dengeki Bunko Fighting Climax (which also features Sega characters (Akira Yuki (the main protagonist of Virtua Fighter series) and Selvaria Bles (one of the main antagonists/anti-villains of Vakyria Chronicles series)).
In BlazBlue: Cross Tag Battle, only Under Night In-Birth characters to have much faster Passive Link chain combo system (the Reverse Beat since Melty Blood) and it’s completely universal. Their Clash Assault are instead mostly uses a simple Hop Dash called Assault to a certain Jump Attack. Most of the characters whose full last name and nicknames are officially confirmed in Arcade and Chronicle Modes of Exe:Late[st], and from French-Bread’s Twitch still not using these in this game, safe for on Vs./Victory Screen Interactions (except for certain characters whose first name are in kanji in Japanese version, such as Hyde Kido), and both Lifebar and Win announcements. Under Night cast’s sprite renders are also much smaller and very pixelated than BlazBlue and Persona cast, which is why cast’s sprites’ size (while still remained pixelated) are being increased to fit in with 3 other series’ sprites’ size for this game, in addition of being given a new mouth moving (during intros, standing (neutral and taunt), and win poses), yet still lack of their eyes moving during standing neutral pose).