An alien girl fell on my head, and now I must save our world by demonstrating great and beautiful love

"What? I've been chosen as humanity's representative, and now I have to prove how promising our species is? But how am I supposed to do that? My plan for entering adult life didn't include anything like this! And what do girls have to do with it? Oh, that's what 'promising' means. Hmm... Hehe... Maybe it's not so bad after all?"