Young Akira has a destiny: He's a shiki tsukai, a warrior with the magical power to control the seasons. He also meets the beautiful Koyomi, another warrior, who is sworn to protect him. For there are evil forces intent on destroying Akira - and the entire universe!

!!This manga contains these tropes:

* EmotionlessGirl: Koyomi Sakuragi
* {{Familiar}}s: The Kijyuus of the Shiki Tsukais.
* {{Fanservice}}: Koyomi's clothing vanishes when she transforms, and she is not at all shy about being seen in her underwear.
* KatanasAreJustBetter: Koyomi Sakuragi can turn into a katana.
* EquippableAlly: Koyomi Sakuragi through VoluntaryShapeshifting.
* OlderThanTheyLook: Akira's mom, Megumi Kizuki, is sometimes mistaken for his sister.
* ThanksForTheMammary: In order for Koyomi to transform into a katana, Akira must touch her symbol which is on her chest.
* WellIntentionedExtremist: Some Shiki Tsukais say they want to save the Earth by killing the majority of humans.