Yakyuu Bunmei Alien

Indifferent student Takatsugi-kun is living an uneventful life, until he meets Niina, a girl who's utterly obsessed with baseball. Though she seems to have nothing but baseball on her mind, Takatsugi finds himself drawn to her. Their relationship progresses smoothly...or does it? An unconventional triple-threat romantic comedy begins!

(Source: MANGA Plus)