1. Your teacher Takao is a weak bitch. At first I sympathized with her because she looked the only sane person in this mess. But then I realized she was easily used by Mr. Hikawa all this time AND was possessed by a fucking entity right in the middle of her philosophic speech, which leads me to believe it's not even hers to begin with.
2. Hikawa sensei was the opposite - at first looked like an egothistic asshole. But after knowing him more (and the conversation at extinct Manta HQ) he looked very reasonable. Like
InD_ImaginE said, it sounded very Buddhist to me too.
3. Isamu is an anti-social wanker who wants to live his life inside his own virtual JRPG dating NPC waifus.
4. Chiaki hinted at suffering at the hand of demons (tentacle rape?) and became a fucking Furiosa straight from Mad Max and wants a world of the strong.
Optional: there's supposedly an extra ending by completing Amala network that overrides all others and is apparently the most badass.