Love is Sickness (コイの五月病, Koi no Gogatsubyō, Carp May disease) is the May event in The Battle Cats.
During this event, a new enemy unit appears: Samurai Doggy! And if any player clears any of the stages during this event, a new cat unit only available during this event: Koi Cat, can be unlocked by chance. The further you progress through the levels, the higher your chances of unlocking the cat unit increase. The player can get the unit with a 100% chance in any of the stages using a Treasure Radar, which can be purchased at any time in the Shop menu.
- 2★ difficulty for this event multiplies enemy strength magnifications by 150%.
- 3★ difficulty for this event multiplies enemy strength magnifications by 200%.
- 4★ difficulty for this event multiplies enemy strength magnifications by 300% and only allows Special Cats and Rare Cats to be deployed.
|English Version||Japanese Version||Translation|
|Stage 1||Liking Love||コイにつかれて (Koi ni Tsukarete)||Being caught in a carp|
|Stage 2||No More Duckface!||満腹！アヒルぐち (Manpuku！ Ahiru Guchi)||Full!|
|Stage 3||Read but No Reply||恐怖！既読放置 (Kyōfu！Sunde 読 Hōchi)||Fear!|
|Stage 4||Online Dating!||最高！ネトゲデート (Saikō ！Netogedēto)||The best!|
|Stage 5||Blocked on FB!||衝撃！ラインブロック (Shōgeki！Rain Burokku)||Impact!|
|Stage 6||Work or Me!||選択！仕事とアタシ (Sentaku！Shigoto to Atashi)||Choice!|
|Stage 7||Let's Just Be Friends||告白！友達に戻ろう (Kokuhaku！Tomodachi ni Modorō)||Confession!|
|Stage 8||Never Give Up!||それでも君にコイしてる！(Soredemo Kimi ni Koi Shiteru！)||Still carp for you!|
- May 1st, 2015 to June 1st, 2015
- May 2nd, 2014 to May 31th, 2014
- The stage makes little sense in English due to its strong reliance on a Japanese national holiday, its associated traditions and a Japanese language pun.
- The 5th of May in Japan is Children's Day, and part of the nation's Golden Week holiday celebrations.
- Koi Cat is indicative of the Koinobori flags/kites/windsocks patterned to resemble koi (carp fish) that are put on display in prominent locations during the festivities. Colourful pinwheels are also associated with children.
- The Samurai Doggy enemy is indicative of the samurai-helmet wearing Kintaro dolls also put on display.
- Koi in turn is a homophone in Japanese, meaning both 'carp' and 'love', hence the romantic themes.