Sentou Hawaii

One day, when Kasumi's bath is in need of fixing, she heads to a nearby public bathhouse. She's the only customer so late at night, and the bathhouse attendant is a beautiful girl named Kiyo. Kasumi is so impressed by the bathhouse and Kiyo that she begins to come back regularly. She soon learns that the bathhouse has been losing many customers to a convenient "Super Bathhouse," and she decides to do what she can for their popularity. But does Kiyo consider Kasumi to be just another customer?

(Source: MangaHelpers)

Included one-shots: Watashi no Kirai na Anata, Under, Transform Girl, 6-nen 3-gumi Suzuki yori