This isn't really an essay than me summing up Makoto's incredibly fucked-up family life!
LET'S START WITH HIS GRANDMOTHER. Grandma decided she wanted to form a cult religion! Surprisingly, it was popular! (I blame it on the Ogami prettiness). Then she had a son, Ogami Hideo, Makoto's dad.
Makoto's dad is the one I have the least canon info about. BACK WHEN HE WAS A TEENAGER, he decided "Let's crawl into a crypt!!!!" and came out ...somewhat changed.
TIMESKIP
Komori Tarou and his sister got kidnapped. On the day they were discovered by the police, Ogami Hideo ripped off his eyelids and committed suicide.
Shouta!Makoto was the first person to discover the body. After that, the entire village was spread with rumours about his father's death and its connection to the kidnapping, but there was no proof. At the same time, mother dearest ran away to another village.
Makoto...spent pretty much all his time in his room, playing guitar and skipping school. Oh, and hating his grandmother (so much that later on in the series he caused her to die)
THEN MASAYUKI COMES TO SCHOOL. And things change! Makoto starts investigating his father's past because he wants to learn more about him! And this investigation leads him to his mother and Ishida Uryuu, the guy she...loves? WELL THE GUY SHE ABANDONED MAKOTO FOR.
Here is where it's sketchy because I've only watched RAWS of this point. BUT BASICALLY, Makoto purchases a switchblade so he can kill his mother. But his mother apologizes to him for abandoning him and Makoto loses his nerve and runs away.
His mom is also not exactly sane as she attempts to do suicide in three different ways, including burning down the house. Makoto finds out and barely manages to rescue her from the flames.
When he visits her in the hospital, mother dearest lost her memory and thinks she's seventeen! And Makoto is Ogami Hideo! At which point, things get bizarre and she blushes at him and he quietly...freaks a bit. HE EMOS ON A BOAT, MASAYUKI COMES TO KICK HIS ASS and he goes back to the hospital. It also turns out that the original person who was meant to be kidnapped (and he was...for a brief period) was Makoto, and not Tarou and his sister! Also, the reason he thinks funny is because the kidnapper hit his head rather hard (instead of his mom dropping him on his head as a baby like he stated earlier)
And his mom in the morning, puts her blanket around him and says, "I'm home"
Makoto quietly cries.