[Unknown Soldier]

Originally Posted by Kitsu

And here we wondered if Beatrice is a part of a split personality. And hey did Rena have a split personality (one moemnt she got Hau~ and the next she went USO DA! lol)
But actually maybe she was faking to trick Shannon into believing her.

Spoiler for higurashi kai, episode 12 minagoroshi:

Rena's apparent split personality was due to Keiichi having paranoid delusions while under the growing influence of Himanizawa Syndrome. She wasn't actually psycho, it was merely Keiichi imagining she was.

That said, apparently Rena can be quite scary when she's angry.