Kongou Mitsuko vs Maiko Plasma: who would win?

Maiko Plasma favored — Slight edge (~55%)

Kongou Mitsuko · Toaru Majutsu no Index · Base

Tier
8-C
Attack Potency
Building Level
Speed
Athletic Human
Durability
Human Level

Maiko Plasma · One-Punch Man · Base

Tier
8-C
Attack Potency
Building Level
Speed
Supersonic, up to Massively Hypersonic+
Durability
Unknown

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