Beretta (Web Novel) vs Onimaru: who would win?

Onimaru favored — Slight edge (~55%)

Beretta (Web Novel) · Tensei Shitara Slime Datta Ken · Post Founding of the Demon Capital Arc

Tier

6-A

Attack Potency

Continent Level

Speed

Massively Hypersonic, up to Relativistic

Durability

Continent Level

Onimaru · One Piece · Base

Tier

6-A, up to HIGH 6-A

Attack Potency

Continent Level, up to Multi-Continent Level

Speed

Ftl

Durability

Continent Level, up to Multi-Continent Level

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