Kihara Kagun vs Mei Hatsume: who would win?

Kihara Kagun favored — Slight edge (~55%)

Kihara Kagun · Toaru Majutsu no Index · Base

Tier

8-A, up to 7-C

Attack Potency

City Block Level, up to Town Level

Speed

Peak Human, up to Supersonic

Durability

Multi-City Block Level+, up to Town Level

Mei Hatsume · My Hero Academia · Base

Tier

8-A

Attack Potency

Multi-City Block Level

Speed

Unknown

Durability

Wall Level, up to Multi-City Block Level

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