Shuna (Light Novel) vs Aradia: who would win?

Shuna (Light Novel) favored — Slight edge (~55%)

Shuna (Light Novel) · Tensei Shitara Slime Datta Ken · Oni

Tier

6-B, up to 1-C

Attack Potency

Country Level, up to Complex Multiverse Level

Speed

Massively Hypersonic, up to Speed Of Light

Durability

Country Level

Aradia · Toaru Majutsu no Index · Base

Tier

6-B, up to 5-B

Attack Potency

Country Level, up to Planet Level

Speed

Supersonic

Durability

Country Level, up to Planet Level

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