I Stole the First Ranker's Soul

Moa Son, an ordinary office worker, wakes up in a dungeon in the middle of the night and awakens as a collecting hunter. After barely making it out alive, she falls into the same dungeon but gets rescued by the first-ranked hunter, Jihan Seo, and becomes bound up with him. Now he’s offering to make her strong on this one condition —
“Promise me you will do your best to kill the bosses of all the dungeons that exist in the world.”
Come again?

(Source: WEBTOON)

Note: Includes three extra chapters.