Lye Batenkaitos vs Umbra: who would win?

Umbra favored — Slight edge (~55%)

Lye Batenkaitos · Re:Zero kara Hajimeru Isekai Seikatsu · Base

Tier

7-B, up to 7-A

Attack Potency

City Level+, up to Mountain Level

Speed

Superhuman, up to Relativistic

Durability

City Level+, up to Mountain Level

Umbra · Bionicle · Base

Tier

7-B

Attack Potency

City Level+

Speed

Massively Hypersonic+, up to Speed Of Light

Durability

City Level+

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