Kamen Rider Black RX vs Souei (Light Novel): who would win?

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

Kamen Rider Black RX · Kamen Rider · End of Series (41-47)

Tier

1-C

Attack Potency

Complex Multiverse Level

Speed

Transonic, up to Immeasurable

Durability

Complex Multiverse Level

Souei (Light Novel) · Tensei Shitara Slime Datta Ken · With Ultimate Skill

Tier

1-C

Attack Potency

Complex Multiverse Level

Speed

Massively Hypersonic

Durability

Complex Multiverse Level

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