Viral vs Nephthys: who would win?

Viral favored — Slight edge (~55%)

Viral · Tengen Toppa Gurren Lagann · Post-Apotheosis

Tier

HIGH 1-C

Attack Potency

High Complex Multiverse Level

Speed

Massively Ftl+, up to Infinite

Durability

High Complex Multiverse Level

Nephthys · Toaru Majutsu no Index · Base

Tier

HIGH 1-C

Attack Potency

High Complex Multiverse Level

Speed

Sub-Relativistic

Durability

High Complex Multiverse Level

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