Gokinjo Monogatari

Takes place before and includes characters from another Yazawa manga – Paradise Kiss.
From Anime News Network:
Mikako dreams of being a fashion designer, so she sets her eyes on attending Yazawa Arts with her childhood friend Tsutomu. But, he looks like a famous rock star and attracts more attention than she’d like, especially from a popular upperclassman. Incapable of dealing with her own feelings towards Tsutomu, Mikako devotes all of her time to a new ‘flea market’ club she’s created with her friends on campus. But, it seems to bring her more into contact with Tsutomu than ever before.
Cameos include Yazawa herself and characters from her previous works.
[From ShoujoMagic]:
Ever since he was small, all the girls in the neighborhood have fawned over Tsutomu Yamaguchi, whose name came from a song and whose adorable face closely resembles the monkey character Monchichi’s. Even back then, it was enough to make his friend and neighbor Mikako sick. Now that he’s a little more grown, Tsutomu looks like the lead vocalist of Manbou, Ken Nakagawa (Midori friend/boyfriend from Tenshi Nanka Ja Nai; we meet main characters from Tenshi on market/fest), and that makes him even more popular with the ladies. But Mikako–now a trendy teen with modern sensibilities–couldn’t care less. Or could she…? Gokinjo Monogatari is a sharp-witted and stylish slice-of-life story!