The One You Shouldn't Have Killed vs Tachibana: who would win?

The One You Shouldn't Have Killed favored — Slight edge (~55%)

The One You Shouldn't Have Killed · Five Nights at Freddy's · Base

Tier
9-C, up to 9-B
Attack Potency
Street Level, up to Wall Level
Speed
Subsonic
Durability
Unknown

Tachibana · Crows x Worst · Base

Tier
10-A
Attack Potency
Athlete Level
Speed
Peak Human
Durability
Athlete Level

A heuristic estimate from normalized VS Battles Wiki stats: tier, attack potency, speed and durability.