Granbell Rosso vs Brain (Kamen Rider Brain): who would win?

Brain (Kamen Rider Brain) favored — Slight edge (~55%)

Granbell Rosso · Tensei Shitara Slime Datta Ken · With Ultimate Skill

Tier

1-C

Attack Potency

Complex Multiverse Level

Speed

Relativistic+, up to Speed Of Light

Durability

Low Complex Multiverse Level

Brain (Kamen Rider Brain) · Kamen Rider · Kamen Rider Brain

Tier

1-C

Attack Potency

Complex Multiverse Level

Speed

Unknown

Durability

Complex Multiverse Level

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