Kamen Rider Century vs Calasmos: who would win?

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

Kamen Rider Century · Kamen Rider · Kamen Rider Century Break

Tier
2-C
Attack Potency
Low Multiverse Level
Speed
Ftl
Durability
Low Multiverse Level

Calasmos · Dragon Quest · True Form

Tier
2-C
Attack Potency
Low Multiverse Level
Speed
Massively Hypersonic
Durability
Low Multiverse Level

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