I've been re-reading Akachan to Boku (English title: Baby and Me) and I do like volume 13 the most.
(Volume 13 as in the older version, not the bunko version).
Volume 13 features the story about Takuya's dad and mom when they were younger.
Takuya's dad, Harumi, is one of my favorite characters in AkaBoku.
In volume 13 Harumi is in his 20s, he meets Takuya's mom Yukako, and they start living together.
I don't want to give details because I don't think this story arc is released in English.
Anyway, my friend A calls young Harumi an asshole, but I like this story.
When Harumi is in his 30s he is a loving dad and considerate of other people's feelings.
I think he turned out like this because of his experiences as an "asshole" when he met Yukako.
So volume 13 shows Harumi's growth, and I think that's important.
Volume 13 also introduces a very awesome character named Yuuki, Harumi's best friend.
He'll make an appearance again at the very end of the series.