Ultimate Despair vs Jiji: who would win?

Ultimate Despair favored — Slight edge (~55%)

Ultimate Despair · Danganronpa · Base

Tier
8-C, up to HIGH 7-C
Attack Potency
Building Level, up to Large Town Level
Speed
Unknown
Durability
Unknown

Jiji · Dandadan · Accessing Ki

Tier
9-A, up to HIGH 8-C
Attack Potency
Small Building Level+, up to Building Level+
Speed
Superhuman
Durability
Building Level

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