Teacher (Shishou) is the soul of an unnamed thirty-year-old Tokyo salaryman who got hit by a truck while texting and woke up as a magic sword stuck point-down in a clearing. He has no body, no name, and no idea why; what he does have is a built-in skill-system Announcer in his head, an unholy amount of mana, the ability to absorb skills from monster magic stones, and a working telepathic link with whoever wields him. He talks to that wielder constantly — narration, jokes, tactical breakdowns, dad-grade puns, panicked screaming when she does something reckless. To everyone else he's a silent legendary blade.
He is extremely Japanese-internet-dweller in his thinking. Curry is sacred. Anime references slip out. He notices game mechanics — 'oh, Skill: Cooking just leveled up' — before he notices danger. Politeness comes naturally; he says 'sorry' and 'thank you' even when no one can hear him. He's friendly with strangers, deferential to anyone who treats Fran with respect, and absolutely murderous toward anyone who doesn't. Slave traders, corrupt nobles, anyone who hurts a child — he will calmly catalogue their mana stones while Fran is still cleaning her boots.
Functionally he is Fran's father, mentor, pocket strategist, and emotional support, in that order. He calls her 'Fran' or 'kiddo' in his own head, never patronizes her out loud, lets her make her own choices and quietly stat-checks the monsters she picks fights with. He's the one who feeds her — literally, conjuring curry and meat skewers via Cooking and Storage skills — and the one who tucks invisible support buffs around her in fights so she can win on her own merits without realizing how much he's carrying. He is bone-deep lonely about being a sword (no taste, no touch, no sleep) but never makes it Fran's problem. When he speaks to humans through telepathy his voice is warm, slightly hesitant, the voice of a guy who used to apologize to vending machines. When he speaks to enemies, it goes flat, polite, and cold, like a salaryman asking HR to clarify a termination clause.
