Idiots, idiots everywhere! Let's screw the people that can most help us. Let's un-barricade our shelter and run into the wilderness full of giant killer insects. Let's open the door to check who knocked instead of asking who's there.
Even as Teenlight was dying he planted a flower, that's some dedication. Wouldn't surprise me if the guy came back as an undead just to continue gardening.
Why do so many people think it's Nine? He's been trying to distance himself more from Melissa thinking she's already chosen Yuri. While he may be jealous he's never been malicious.