RanoTano

The story centers on Yakumo Atae, a first-year student who knows the hidden secret of his fearsome classmate Tsurugi Yabusame — while she is the school's strongest girl, she is also a budding light novel author under the penname Mio Himemiya. Tsurugi is stuck in a huge slump while writing her new romantic comedy. Yakumo's cousin Kokona Atae happens to be Tsurugi's editor, and Kokona suggests that Yakumo and Tsurugi become a couple so that Tsurugi can know the experience of romance.

(Source: Anime News Network)