Rainbows After Storms Vol. 02 by Luka Kobashi

The couple cherishes each other while hiding their relationship from their friends. Chidori can't help but cheer on her super-cool girlfriend during gym class, and Nanoha wants to flirt while the rain pitter-patters on the umbrella they're sharing, no matter who might be listening. The seasons pass from spring to winter, but their relationship only grows warmer as time marches on.