Aoi Kaguragi vs Miquella the Kind: who would win?

Miquella the Kind favored — Slight edge (~55%)

Aoi Kaguragi · Kaiju No. 8 · Post-Second Division Training

Tier
7-A
Attack Potency
Mountain Level+
Speed
Unknown
Durability
Mountain Level+

Miquella the Kind · Elden Ring · Base

Tier
7-A, up to 3-B
Attack Potency
Mountain Level, up to Multi-Galaxy Level
Speed
Sub-Relativistic+, up to Speed Of Light
Durability
Multi-Solar System Level, up to Multi-Galaxy Level

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