Koi Cupid

Koi Cupid is a manga written and illustrated by Mia Ikumi. The story revolves around three young cupids, Ai, Ren, and Koi.

Training to become full-fledged angels, they go on special missions to bring people together using The Power of Love. However, it isn't as easy as one would think; sometimes the humans are uncooperative or disbelieving. And then there are the demons...

According to The Other Wiki, it's a Seinen manga.

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This manga contains examples of:

 * Alpha Bitch: Ren has traits of this, being a spoiled showoff. However, she does complete missions faster than anyone.
 * Applied Phlebotinum: Each cupid has a magical item to assist in bringing people together. Ai's is love letters, Koi's is a bow and arrow, and Ren's is scissors.
 * Though subverted with Ai, whose magical item doesn't seem to do anything; she uses the letters as a symbol to let her complete the missions.
 * Catgirl: Lizette's demon outfit has cat ears. She also has Cute Little Fangs.
 * Cats Are Mean: Lizette calls forth a cat familiar to eat the baby bird representing a couple's love; afterwards she gloats that they will never get along now.
 * Cute Kitten: Sister Yuuri, the angel supervising the cupids, is a cat with two tails.
 * Lizette's demon costume has cat ears.
 * Honorifics: Ai talks in a childish way and most often uses the suffix -tan. Koi talks more formally, using the suffix -senpai.
 * The Messiah: Ai can connect to almost anyone, and her greatest wish is to be friends with people. She even warmed Lizette's heart.
 * No Export for You: Only one volume of five was released in America due to the publisher, Broccoli Books, going out of business.
 * Our Angels Are Different: Some of the types of angels they can become are guardian angels, and grown-up cupids. Cupids exist to bring couples together so their baby can be born.
 * Red String of Fate: Literally, as strings are seen connecting people together. If necessary, the strings can be cut with magic scissors.
 * Sugar Apocalypse: The cute character designs contrast with the serious tone.
 * Sugar Bowl: The angel world.
 * Sweet Dreams Fuel
 * The Power of Friendship
 * The Power of Love: They are cupids.
 * What Could Have Been: Since the publisher went out of business, it's unlikely people in the U.S. will ever get to read Volumes 2 through 5.
 * Wide Eyed Idealist: Ai, again.
 * You Gotta Have Blue Hair: Ai, who actually has blue hair. Also, Koi has pink hair.
 * You're Nothing Without Your Phlebotinum: Cupids can't give up their pochettes; if they do they are disqualified from training. Lizette is aware of this, and says she'll be Ai's friend if she throws her pochette away. Ai attempts to do this and almost drowns trying to recover it.