Is It Wrong to Try to Pick Up Girls in a Dungeon? On the Side: Sword Oratoria, Vol. 8 (light novel) — Fujino Omori

Bete Loga-
-Even when compared with the rest of Loki Familia, his steadfast belief that only the strong matter is considered extreme. In the wake of the withdrawal from Knossos, his callousness towards those who died in battle has isolated him from the rest of the familia but there is more than meets the eye...

When an Amazon named Rena suddenly appeared before Bete, her aggressive attempts to win him over ever so gradually lead to them to begin...living together?! Bete can hardly believe it himself, but soon his interactions with the girl bring up old memories of companions lost. However, the assassin's blade that stole his comrades from him before has begun to loom once more!