Yuiko Kubozuka is a high school student who loves animals with a burning passion, though animals unfortunately hate her and flee from her whenever possible (usually causing damage to her in the process), prompting her friends to say that she should focus that energy on a boyfriend. She, of course, isn't all that interested, until one day, while attempting to retrieve her (unwilling) cat from the local park, a mysterious boy with a wild look in his eyes brings it back down with little trouble. She thinks little of it until the next day, when the boy transfers into her class. His name is Leo Aoi, and, despite his fierce expression, he's really a sweet, naive, gentle hearted teen - at least, until he sees blood. When Leo sees blood... Well, let's just say that [[BerserkButton he isn't exactly human when he sees blood...]]

Because Yuiko is the first to see beyond his frightening expression, Leo quickly becomes strongly attached to Yuiko, who is his first friend. Yuiko is unique in her ability to calm Leo down when he goes into one of his rages, and slowly, they begin to fall in love. However, soon, Leo's past starts to catch up with him, and it threatens to rip the couple from each other's arms.

!!Tropes found in this work include:
* {{Adorkable}}: Leo, Leo, Good God Leo!
* AdultFear: Attempted rape on Yuiko. The rapist pretends to feel ill, and Yuiko helps him. Once she gets him near a bench, though...
* BerserkButton: Literally when Leo sees blood.
* CooldownHug: Yuiko to Leo. She's the only one who can do it, too.
* CuteLittleFangs: Who else but Leo?
* DarkIsNotEvil: Leo has black eyes and hair, but he isn't a bad person.
* DisappearedDad: Nobody knows where Leo's father is. [[spoiler: He shows up in the second volume for some plot movement.]]
* DontTryThisAtHome: When Leo climbs a telephone pole to get a scent on a missing dog, Yuiko briefly [[BreakingTheFourthWall breaks the fourth wall]], saying to the readers, "Don't try this at home."
* FaceOfAThug: Leo. With the sweetest possible personality behind it, of course. Also, Boss and his group.
* FriendToAllLivingThings: Leo. Yuiko tries to be, but, well, she's a little too enthusiastic...
* GoodScarsEvilScars: Leo has several scars on his shoulder, chest, stomach and back but they do not in any way detract from his appearance.
* HandsOnApproach: Leo gets behind Yuiko and calms her down so some birds will land on her.
* HiddenDepths: Boss, who appears to be a stereotypical yankee at first glance, but is actually a very kind guy who cares a lot about his friends, patrols the neighborhood when there's an attacker on the loose, and takes care of an abandoned German Shepard. WordOfGod says that his biggest crime is not adhering to school uniform regulations.
* ManChild: Leo: he's actually older than Yuiko, yet still has a very innocent behaviour and becomes fascinated by mundane stuff like hamburgers or soda.
* NobleSavage: Essentially how Yuiko imagines Leo was during his time "living in the wild". It's noted that it was probably completely different, though.
* RaisedByWolves: Leo, of course.
* SavvyGuyEnergeticGirl: Inverted, except around animals.
* {{Yandere}}: Sasamoto's girlfriend.