So the MMC dies or almost dies when the FMC lands on earth and uses her powers. He gets her heart which also includes powers. She goes into hibernation until second year of high school and he is a first year. Later on we find out she is the perfect clone of an old dead queen and all her imperfect clones are dead and MMC has the kings heart. He also kills his twin and I think his grandpa runs a bookstore.

[img]http://media.otakuzone.com/store/album/5/32765/T129652429476d1322ca36edc198f2adf9dd1022b524f.png[/img]

It's Hitoribocchi no Chikyuu Shinryaku.