Samishigariya No Love Letter summary:

Yuuki is a university student bored with his ordinary life. One day after returning home after class, he finds a strange chocolate tin in his bag. Inside it is a letter with "I want a friend" written on it by an unknown sender. When he writes a reply as a joke, the next morning another letter is inside it...Also included is Haru, Hinata no Koi and Koiiro Milky Way.