Kuchi Ga Saketemo Kimi Ni Wa

i fail to understand that the first 3 chapters is the brown-haired kid Kouichi that became an elementary school teacher, and the 4th chapter onwards is the raven-haired highschooler Kouichi. Why?

two story in 1 manga? it's so complicated

So miruku's brother looks like villain izuku midoriya from an alternative Boku no hero academia

.

😱😱😱 NOOOOOOO, was he lying? I need to know 😫