Straightforward multiple stories with 2 chapters for each couple.
1-2 Ao x Kurose: Ao has been in love with Kurose who always picks up his student from Kindergarten. He mistakes him for a single father. His twin brother Midori (who's always bad with boys) tells him that he has a new boyfriend named Haizaki (Kurose's last name). Midori tells him while drunk to go on his date instead so he pretends to be his twin brother not knowing that Kurose knows and has been in love with him as well.
3-4 Midori x Shirase. Love story between the first couple's twin brothers. Midori meets Shirase in an amusement park after Aki (Shirase's son) mistakes him for Ao. They get to spend time together and become lovers lol. Main concern was gender issues since Shirase was straight at first but the conflict was actually because Shirase was concerned that his sexual drive might break Midori
5-6 Timeskip story between Aki (son from previous stories) and his preschool classmate Akane. Akane has been in love with Aki since kindergarten days but gets turned down since Aki "loves" Ao-sensei. Because of this Akane has avoided Aki. Later on they find out that their feelings were mutual and Akane finds out that Ao is already Aki's uncle's lover
Kuro X Koi