Tatsumi

is a young traveler that Mirai Sarutobi meets in the Land of Hot Water.

Background
After the death of her mother - her only remaining relative - Tatsumi began visiting hot springs that her mother had spoken well of when she was alive. While traveling between hotsprings she met Ryūki, who offered to help her see her mother's spirit if she brought him new followers.

Konoha Shinden: Steam Ninja Scrolls
Tatsumi meets Mirai Sarutobi at a hotspring and they become fast friends. While enjoying the hotspring's waters late one night, Tatsumi asks Mirai if she would like to speak with anyone who's dead. Mirai wants to see her dead father, so Tatsumi invites Mirari to join her in communing with the dead. She leads Mirai into the mountains, locates the cave where Ryūki and his followers are assembled, and introduces Mirai to Ryūki.

Tatsumi encourages Mirai to drink some water that Ryūki offers her, which he says will prep her for seeing the dead. Mirai suspects the water is drugged and refuses, revealing herself as a ninja of Konoha and accusing Ryūki of being responsible for a series of kidnappings in the area. Ryūki confesses and states his intention to sacrifice Mirai, Tatsumi, and the other girls he's kidnapped to his god, Jashin. Tatsumi is horrified to hear this, but Ryūki insists that he truly can help her meet her dead mother; he then tries to kill her so she can meet her mother in the afterlife.

Mirai saves Tatsumi from Ryūki and, with help from Kakashi Hatake and Might Guy, defeats him and his followers. Tatsumi apologizes to Mirai afterwards for nearly leading her to her death, but Mirai is grateful for the experience: she has found a purpose in life by protecting her friend, Tatsumi. Tatsumi vows to make the most of the future Mirai has secured for her.