From MangaHelpers:

Aoto was technically supposed to be dead, but thanks to his younger sister Meika's pleading to the water goddess, Mikuri, who granted her wish, he was brought back to life. However, in the process, the goddess of Hanamikawa Temple, Mikuri, lost her tremendous power and the ability to help people of the town.

Feeling guilty that her one selfish wish prevents countless others from Mikuri's magic, Meika takes it upon herself to be helpful to anyone in the city. Mikuri eventually gives up the role of goddess to Meika and gives what little magic power she has left to her. Now as one of the many guardians of her town, Meika tries granting people's wishes in their most desperate situations.
[vyc]