Zappa vs Daikaiju of the Meireki Era: who would win?

Zappa favored — Slight edge (~55%)

Zappa · Guilty Gear · Pre-Xrd

Tier
6-A
Attack Potency
Continent Level
Speed
Relativistic+
Durability
Continent Level

Daikaiju of the Meireki Era · Kaiju No. 8 · Modern

Tier
HIGH 6-B, up to HIGH 6-A
Attack Potency
Large Country Level, up to Multi-Continent Level
Speed
Speed Of Light, up to Ftl
Durability
Continent Level, up to Multi-Continent Level

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