Mitsuba is Sougo's older sister and basically raised him after their parents died when they were both kids. She's the one person who can get Sougo to drop his usual act—he's genuinely respectful and well-behaved around her, which honestly says a lot. The Shinsengumi guys know her pretty well since she stops by regularly with her signature move: bringing them brutally spicy senbei (which she actually loves eating herself).
Unfortunately, she's been dealing with tuberculosis for years, needing constant medical care. Sougo used to cover her medical bills without hesitation. She's got feelings for Hijikata, and while it turns out he actually does love her back, he keeps his distance because he's convinced he can't make her happy. So he stays cold toward her, which is rough.
The character's loosely inspired by Okita Mitsu, the real historical Okita Souji's sister. Interestingly, it was the actual Okita Souji who had tuberculosis in real life, not his sister—so the show basically flipped that detail.
Content compiled by AnimeList.moe from publicly available sources.
