Yagami-san wa Kakushitai!!

A first-year high school boy, Nagumo Hassaku, gets called "Hakushaku-sama" because of his tall stature and intimidating appearance. He wants to make friends, but he has trouble talking to people, so he lives his high school life as a loner. Until one day, when he accidentally discovers the secret of Nora Jashin, the most beautiful gal in his class...

When she gets excited, a large tail pops out!

A heartwarming love comedy between a monster-gal and an introverted boy!
(Source: Futabasha, translated)