Lefi is the top wife and essentially convinces nell to confess to yuki later in the wn, lefi does admit that she wouldn't mind having yuki all to herself, but she'd much rather they all keep staying together (lefi has been alone for centuries, so the happiness of being with everyone happy is far more important to her than mere jealousy, and she loves all of the residents of the dungeon like family, trying to force them to deny that kind of relationship would just cause undue issues in lefi's eyes so she's the main instigator behind it after she figures out nell's fallen in love with him), currently he's officially married to lefi, nell (the last 70 or so wn chapters have focused heavily on yuki and nell with a mix of adventure and lovey dovey moments) and lyuu(wolf girl), though lyuu's was borderline accidental, as for the others, leila hasn't really shown much signs of romantic interest, illuna is saying she will hold yuki to his marriage promise when she get's older, shii (slime girl) also seems to want to marry him when she grows up, and the princess we'll meet in a few chapters in the manga is also heavily infatuated with him (much to his chagrin, as lefi and nell like to tease him that he's a lolicon), ironically the one most against the harem was yuki, it took a fair bit of time for him to finally accept it.