Undertown, Volume 1

After sneaking into a black-market auction, the thief Kalim accidentally steals one of the most highly priced goods: a beautiful demi-human with beast ears and a tail named Asena. Now, Kalim has to take responsibility and shelter Asena in his home for one month until the ship that can take him back to his homelands arrives. Asena, who despises humans for the way they’ve subjugated demi-humans, treats Kalim coldly at first, but then something Kalim never could’ve expected happens: Asena goes into heat! 
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NOTE: This book contains mature themes and explicit sexual content, including situations involving dubious consent. It is not intended for anyone under 18 years of age.

Tired of the fast-paced city life, Izuki has agreed to take care of his uncle's house in the mountains, which are said to be "visited by yokai." 

Izuki, dismissive of the superstition, goes exploring — only to be attacked by a yokai in the woods. He's saved by a beautiful man named Haku, who claims to be the incarnation of a komainu guardian dog. He pledges himself to Izuki and begs him to be his master. Izuki refuses at first, wanting to return to the city as quickly as possible, but is swayed by Haku's lonely eyes and brings him back to the house. Gradually, he falls into a comfortable rhythm with the pushy but devoted Haku while living under the same roof, and Izuki wonders if he really wants to return to the city as he thought. 

However, Haku harbors a secret that could put Izuki's life at risk. Will Izuki and Haku come together in the end, or will Haku succumb to the loneliness that he's held at bay for centuries...?

NOTE: This book contains mature themes and explicit sexual content, including situations involving dubious consent. It is not intended for anyone under 18 years of age.

"Our two leads understand what they're missing out on in life, and finding it in each other was cute. I also credit the narrative for how it wraps up the story threads by the end. When we finally reached that point, I was admittedly emotional." — MrAJCosplay

"Are you attracted to the idea of a man who you so enamored that he can't control himself? A love interest who is more beast than man? So strong and mysterious that he might even be dangerous? That's what A Beast's Love Is Like the Moon has to offer: a supernatural romance with Twilight vibes, where the love interest is an ancient and unknowable creature who perplexingly wants nothing more than the first young ingenue to show up at his doorstep." — Lauren Orsini