Kang Maru is Mu-Young's friend as well as his only connection to the chachaoong world at the start of the story. Maru helps him gather information about other chachaoongs as a way to pay a previous debt.
Maru appears as a young man in his early twenties. He has short, somewhat shaggy blond hair and amber eyes, and is always seen wearing a black shirt with red sleeve garters, a red tie, and red trousers.
Maru has an easygoing, cautious personality, and dislikes fighting. He is very fond of women and can be perverted at times (such as insisting on wearing sunglasses so no one can see him eyeing up potential girlfriends). However, he does not seem to have any luck with women, since he has been single his entire life. He is a devoted friend of Mu-Young almost to the point of being a follower or lackey.
Maru's primary ability so far is enhanced hearing, similar to that of Mu-Young's extreme visiual acuity. Not only can Maru listen in on conversations happening in buildings some distance from where he is, but he can hear things such as irregularities in the heartbeats of people passing by him on a crowded street.
When summoning weapons, he specializes in firearms rather than blades; his guns (though small) have far more power than a normal weapon of the same size as well as the ability to shoot fire.
- Mu-Young - Maru's only significant relationship to date, he appears to be a very loyal and close friend of Mu-Young, willing to put himself in harm's way to do favors for the other man.
- Sora - They appear to know each other fairly well, and are on friendly terms with one another.
Nothing is known of Maru's past prior to the start of the story other than that he wandered around until he "was caught" by Mu-Young, and became his only connection to the rest of the chachaoong community for a while. The two of them are good enough friends to rely on each other for favors and protection—Maru refers to Mu-Young as "Hyung-nim". Mu-Young treats Maru much like a younger brother, including forcing him to study for and achieve his GED.