From Hachimitsu-scans:
In the distant future, humanity is now only made up of women. Kohane Sumino has just enrolled into the prestigious Shirasakuya Academy that contains within it a secluded courtyard garden maintained by the Gardening Club. Legend has it that if two people pledge their love for each other underneath a pair of trees in that garden, they will be bound for eternity. Kohane seeks out the garden on her first day of school, where she meets Rekka Hanatsuka, the friendly self-proclaimed acting president of the Gardening Club. Although Kohane proves to be fairly popular early on, she soon learns that paradise is not without its thorns.