Hyde Kido (Unknown Actor), is the main character of Under Night In-Birth and its updates.
He returns in BlazBlue Cross Tag Battle as a playable character and as one of the four main protagonists.
A normal high school student living alone, he was drawn into the Hollow Night, a phenomenon which saw him nearly killed by invisible beings called Voids. He was saved thanks to the timely intervention of Linne, a nearly-century old being in the body of a young girl whom he saved from a common thug back in a daylight, and her ally, the giant Waldstein. The event caused Hyde to awaken to becoming an In-Birth, allowing him to harness the powers of EXS, the source of all things. Grateful, he has since dedicated himself to helping her cause and ending the Hollow Nights for good.
Sometimes in the past before becoming an In-Birth, Yuzuriha Sougetsu, who few years older than him use to be his childhood friend, until they are separated after a “certain incident” where Hyde regretted to remember it.
At time of becoming an In-Birth, Hyde’s luck becoming much worst, such as being followed by Linne’s fallen older brother Kuon and noticed by Amnesia’s leader Hilda, who wants to meet him for a bet in an upcoming Hollow Night War. The worst part is that he is accused by a middle schoolgirl named Nanase for sexually harassing her and transformed her into an In-Birth, even though it was actually her fault for this misunderstanding and the dumb situations she is in, as Hyde was only trying to save her from the Voids attacks on her, by not turning her into an In-Birth, despite feels responsible for her rude behavior. Hyde also adopts Vatista, one of Nights Blade’s old associates to stay in his home until she complete her mission.
- Hyde has color palettes of the following characters: Sol Badguy (Guilty Gear), Ragna the Bloodedge, Yu Narukami, Linne, Ruby Rose, and Steven Universe (Steven Universe).
- Hyde's title, Unknown Actor, refers to Hyde being the mysterious person who follows the Princess of the Night Blade. His title is also the name of main theme for Under Night In-Birth EXE: late [st].
- All known members of the Night Blade (Including Hyde) all have Steven Universe™ color pallets in their Color 13 slot: Hyde: Steven Universe, Linne: Garnet, Waldstein: Amethyst, and Vatista: Rainbow Quartz.