Twin Spica, Volume 05: 06/11/12
Twin Spica Volume 05 by Kou Yaginuma has two plot threads: a three day training challenge and puppy love friends, past and present. Asumi and her classmates are about to start their second year but they have one last test.
The book starts with a present day friendship brewing between Asumi and an orphan boy who shares her love of outer space. He was orphaned by the Lion crash and feels compelled to act as if he's anti space exploration, even though he secretly loves rockets.
Their friendship is paralleled with a flashback romance between Mr. Lion and the mother (?) of the ill rich girl. It explains the girl's love of space and gives insight to how frail she might actually be.
Mostly though the book is about survival training. The kids are dropped into the forest and have only a few days to figure out where they are and find their way to the rendezvous. Although it isn't stated outright, it's implied that if they don't make it by the deadline, they won't make it to the next year of school.
The book ends casting doubt on whether Asumi will be able to get to the finish line in time.