Hibi Chouchou + Hirunaka no Ryuusei crossover in the May 5th issue of Margaret in 2014.

Hirunaka no Chouchou - a Shocking Day for New Discoveries
A shopping mall date with Suiren and Kawasumi. But… Suiren gets lost?! She and a small girl find themselves at the Lost Child centre where suddenly Suzume and Mamura come along!
Released as chapter 75.4 in volume 12 of Hibi Chouchou.

Hibi Ryuusei - Suzume’s Parallel School Diary
The Suzume who steals everybody’s attention at the high school entrance ceremony. Though she's no great beauty, she does things at her own pace and is a hot topic amongst everyone. In the middle of this, the only person who doesn’t notice her, Kawasumi – will he become interested?!