Ambassador Darkness vs Riku: who would win?

Ambassador Darkness favored — Slight edge (~55%)

Ambassador Darkness · Kamen Rider · Base

Tier

1-C

Attack Potency

Complex Multiverse Level

Speed

High Hypersonic, up to Speed Of Light

Durability

Complex Multiverse Level

Riku · Kingdom Hearts · KH3D

Tier

1-C

Attack Potency

Complex Multiverse Level

Speed

Athletic Human, up to Infinite

Durability

Complex Multiverse Level

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