Ruka To Ita Natsu

toono-kun’s life has gone out of control, all due to a strange accident that he can’t explain. there was a flash out in the school yard where his younger sister yayoi was doing track and field, and a number of people were injured, including yayoi. yayoi was lucky and got out of the hospital the next day – only she doesn’t act like herself anymore. what toono has discovered is that his little sister is gone, and has been replaced by a soldier named luca from 31 years in the future – and he alone knows it!