Mesugaki Summer Life

Your younger sister, Tsukino Yuzuha, is an excellent student who excels in both academics and sports. Due to this stark contrast, you, an ordinary brother, have kept your distance from her. After the school's closing ceremony, you returned home and accidentally caught a glimpse of your sister in her underwear. "You get excited by seeing your little sister in her underwear, Onii-chan?" However, that honor student sister of yours... turns out to be a cheeky brat! "Onii-chan, your summer vacation belongs to Yuzu." Now, with this cheeky brat having leverage over you, and you being at her mercy... a sweet and naughty summer vacation between the two of you begins. [Translated from DLsite]