Okay, so Reiichi has inferiority complex, despite the fact his parents encourage him whatever he does anyway and support him.
He is jealous of Otone it's not him be praised by his brother, that despite her clumsiness as Nico is, is loved by Tsugumi that sees her as perfect maid.
Then in overall catastrophic event tells Otone to run into fire because Tsugumi was probably still in the house, killing her. It's like he didn't pull a gun to her head, but gave a gun and said why don't you shoot yourself.
Man, that's fucked up...
Thanks for scanlation!