它 was the original character for snake: a serpent's swaying body, later given a roof. Ancient greetings asked 无它乎？'no snakes?' — snakebite being the nightly worry of mat-sleeping farmers. When 蛇 took over snake duty, 它 was freed to mean 'it'.
Chinese third persons split by script, not sound: 他 he, 她 she, 它 it — all pronounced tā. The ear can't tell them apart; only the page can. 它 covers animals, objects, and abstractions — your cat is 它 in writing, family in spirit.
A snake coiled under the roof 宀 — the original IT you asked about nightly.
'无它' — 'no snakes' — evolved into meaning 'nothing else / no second thoughts': loyalty vocabulary descended from reptile checks.