Tsubaki is Black Star's weapon partner, a Dark Demon Blade capable of transforming into various ninja tools—shuriken, smoke bombs, and eventually a katana in later chapters. She's known for putting up with Black Star's loud, obnoxious personality, though fans often note she actually likes that about him, even when it exhausts her. What really defines her is her forgiving nature and her tendency to help people without hesitation, even when she has no clue what she's doing. Dr. Stein once observed that her soul is unusually cooperative with plenty of room to accept others, which basically sums up why she keeps sticking by Black Star despite everything.
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