1x13 - Starry Sky

Suzuya reflects on his past with his childhood friends Tsukiko and Kanata and how he had always wanted to protect them ever since they were young. Suzuya always took care of Tsukiko and Kanata thus making him the "mother" of the two. Wanting to be able to do something for them, he worked hard to be able to cook well and so forth. He meets Kazuki Shiranui who is friends with Kanata and Tsukiko and eventually the four become an inseaperable group until an incident involving Kazuki and Tsukiko separates them and Tsukiko loses her memory of Kazuki. In more present day, when the three first move into highschool they meet up with Kazuki again though Suzuya still can't forgive what he did in the past.