Yongwangnim Daegijung

A world where humans and mermaids coexist. Dong-I, a rabbit mermaid, applies for the Dragon King's critical condition after hearing the news that the government is offering a huge reward to mermaids who provide the rabbit's appendix. But the contract is strange...? He has to inject the rabbit mermaid Gong Ja-Ran's... into his body?!

(Source: Lezhin, translated)