Levi Ackerman (SnK) vs Thorfinn (Vinland Saga)

This is young edgelord Thorfinn

Round 1 : Levi without ODM gear on ground

Round 2 : Levi with ODM Gear

Round 3 : Both with ODM Gear with Thorfinn having trained for 10 years with them

Round 4 : Thorfinn having trained for 10 years with ODM Gear vs Beast Titan

Thorfinn

Levi wins all 3 rounds.

Thorfinn has a chance on the ground, though I forget most of Levi's ground feats, if he has any at all to speak of, except for maybe that small scuffle with Kenny's squad. Second round clear victory for Levi. Third is a hypothetical that can't be debated properly or worth any while... but I'd like to think Thorfinn could win, he did become a high tier in verse at a young age. I only know anime thorfinn tho, maybe manga presents some more precise evidence

Levi blitzes all rounds

I honestly can barely think of any feats from Levi without 3D maneuver gear, but Levi's post timeskip gear should include guns and thunder spears which likely give him the edge. He certainly wins round 2. Thorfinn just doesn't have experience with a comparable opponent and lacks the mobility to keep up.

Rounds 3 and 4 are speculative, not much to really discuss. We have no idea how skilled with 3D gear Thorfinn would be.

Levi al rounds. He sits on a higher tier