Kuni Mitsu was born the first child to Kuni Mia(mother) & Kuni Renji(father, deceased). Her father Kuni Mitsu was born the first child to Kuni Mia(mother) & Kuni Renji(father, deceased). Her father died when Mitsu was still young and as is normal among the Crab Clan her mother remarried the next year to Kuni Hideo, whilst at first Mitsu didn't really get along well at all with her stepfather, over the years she has grown more accepting of him and gets along reasonably well with the man, though of her parents Mitsu still gets along more with her mother then Hideo.

When Mitsu came of age to start her studies the Kuni Witch Hunter, Kuni Shizuka took the young Mitsu as her student, teaching her the traditions of the Kuni Purifier and following Mitsu's gempuku she remained with Shizuka for a while longer, learning more from the seasoned Witch Hunter in hopes of one day becoming one herself.

The most notable things about Mitsu's appearance beyond the typical white & red make up the Kuni family is known and her short stature, is a prominent scar along the left side of her face starting up on her forehead and narrowly missing her left eye as it runs down her neck a little ways. Whilst the wound doesn't cause to much discomfort anymore speaking and use of her mouth causes mild discomfort at times. The scar is from a injury she sustained during a trip she took into the Shadowlands with her Sensei Kuni Shizuka & fellow student Yogo Ayaka as the three where on the trail of a Bloodspeaker, they found the Bloodspeaker and killed them and their minions aiming to rescue the two samurai they had kidnapped Moto Kadan & Doji Namika, but in the fighting one of the two samurai the Bloodspeaker had kidnapped the Unicorn Moto Kadan was killed & Kuni Mitsu herself was grievously injured.