Kuroyoru Umidori vs Eria the Water Charmer: who would win?

Eria the Water Charmer favored — Slight edge (~55%)

Kuroyoru Umidori · Toaru Majutsu no Index · With Extra Arms

Tier

8-A, up to 7-C

Attack Potency

Multi-City Block Level, up to Town Level

Speed

Peak Human, up to Supersonic

Durability

Street Level, up to Town Level

Eria the Water Charmer · Yu-Gi-Oh! · Raging Eria

Tier

8-A

Attack Potency

Multi-City Block Level

Speed

Supersonic

Durability

Wall Level, up to Small Building Level

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