Ki wo Tsuke na yo, Onee-san.

The OL Tae Honda went swimming at the community pool, but her lack of exercise caused her to cramp up in the water, when she was saved by a tall, beautiful girl Mai Igarashi. Feeling attracted to her savior as she left the the pool, Tae saw Mai come out carrying an elementary school backpack…
Note: Includes 4 extra chapters.