Kusottare Ever After

In their fight to win over the princess, rivals Oogami, a werewolf, and Nomiyamada, a vampire, have been cursed with immortality and unaging youth. Hundreds of years have passed by as they await the reincarnation of the princess who holds the key to breaking their curse, and now their once fiery rivalry has turned into something leisurely instead.

As he starts to feel desperate, Oogami decides to at least have his own household to which Nomiyamada said: "If you're gonna marry someone, then why not just marry me instead?" With Nomiyamada's proposal, Oogami suddenly finds that his lips and bottom half, that he has kept protected the past hundred of years, are now in danger of getting stolen!!

(Source: Kasakura Shuppansha, translated)