Isekai Shihai no Skill Taker: Zero kara Hajimeru Dorei Harem

Konoe Yuuto is a genius martial artist who is summoned to a different world where slave trading is legal. There, using his "Skill Taker" cheat ability, he steals the abilities of monsters he defeats, and starts building a slave harem while hoping to live a carefree life after retirement.

(Source: Novel Updates)