I've watched the anime and the songs, and I've read the first LN. (Yes, I know the anime deviates from the main story a bit.) Do I have the story here about right? Lemme explain how I think everything plays out.

First, we've got Azami the Medusa. Her tale plays out like the storybook in Mekakucity Actors says, and the Fantasy Forest episode continues it. Blah blah she creates the Heat Haze, blah blah she leaves Tsukihiko and Shion alone in the world of the living, blah blah Shion and Marry die. She makes the Heat Haze swallow them up, then gives Shion the queen snake (who gives it to Marry), allowing Marry to live again. But that makes Azami lose control of the Heat Haze, making it swallow up anyone who dies on an August 15th. Marry spends a hundred or so years alone in her forest.

Kido dies in a house fire and gets the snake of Concealing Eyes, eventually learning to control it. Kano and his mother get killed by thieves, and he gets the snake of Deceiving Eyes because of blah blah physical abuse. And Seto dies saving his dog from drowning, earning whatever his power is called. The three go to an orphanage and all get adopted by the Tateyama family.

Ayano makes the Blindfold Gang for them. Her parents go off to research the story about Azami, but they die in a landslide. Only Kenjirou comes out of the Heat Haze, complete with the snake of Clearing Eyes (which does... what, exactly?), the one that manipulated Azami into making the Heat Haze in the first place. Ever since then, he acts weird at night, so Ayano and Kano start investigating.

Meanwhile, Takane and Haruka pass time as the only students of Kenjirou. At the school festival, they meet Kano, Kido, Ayano, and Shintarou, eventually making friends with the latter two. Then, one August 15th, Kenjirou kills Haruka and Takane. They both enter the Heat Haze and gain powers that let them live on in new bodies. But Haruka (now Konoha) loses his memories.

That same day, Ayano confronts the snake of Clearing Eyes. To thwart his plans to create a Medusa in the world of the living, she commits suicide, enters the Heat Haze, gets a power, and never comes back. Kano is distraught.

The kids run away from the Tateyama family, continuing the Blindfold Gang on their own. At some point, Seto finds and recruits Marry.

This is where the timeline splits into Route 1 and Route XX. In Route XX, Kano disguises himself as Ayano and bullies Shintarou for his (perceived) role in Ayano's death. Eventually, Shintarou, still unable to get over Ayano's death, kills Ene somehow and then kills himself. Later, the snake of Clearing Eyes ditches Kenjirou and possesses Konoha instead, using his body to kill everyone. Marry turns back time somehow.

In Route 1, Shintarou breaks his keyboard, so he has to go get a new one at the department store. He gets shot, Blindfold Gang rescues him. Meanwhile, Momo (who got her power a while ago when she nearly drowned) gets recruited into the Gang a la Kisaragi Attention. But Marry destroys her phone, so they have to go get a new one, helping Shintarou out with his plan at the department store.

August 15th. The gang goes to the amusement park. Meanwhile, Hibiya and Hiyori are caught in a time loop where one of them ends up dying, and they each try to save each other every time. Konoha is caught in the loop too, but all he can do is watch in horror. Eventually, the loop ends with them both dying, but only Hibiya comes out of the Heat Haze.

Konoha shows up at the amusement park, presumably suffering a mental breakdown because he just watched his friends die a zillion times. He tries to shoot himself, but Shintarou intercepts the bullet and dies. Shintarou enters the Heat Haze and gets the snake of Retaining Eyes. While he's there, Ayano passes her power on to him.

Then... something happens, I guess? I dunno what comes after this. Could you help me fill in the blanks, and correct whatever I got wrong? Like, why did Kuroha kill everyone in Route XX? And what happens after the amusement park in Route 1? I'm pretty sure I've got everything right up until the timeline split.