Mamono Musume - Life with a Lamia

Years ago, Light made a promise with his childhood crush, swearing that they would one day meet again to get married. Now, years later, he is surprised to find her standing on his doorstep! She's ready to pick back up where they left of, but there's a problem... she isn't quite what he remembered.

She a stubborn tsundere lamia named Leimia, who is has arrived to bring her husband-to-be back to her tribe. Light isn't sure how to react to a lamia at his doorstep, let along one who wants to marry him. Light refuses her invitations, but Leimia won't give up that easy! She decides the best way to convince him is to move in with him. Not only that, she is determined to make him fall for her, and will do whatever she can to achieve that!

[From Jast USA]