That final scene with Erin is so good. He's so fucking cute there's no way in hell I'd ever take the route to kill him, I'll choose to add him to the harem every time. Looking forward to seeing where the path of turning him into an actual girl leads, although him staying a trap would be fine too. Mars is the hero of this story and in my headcannon, his end goal will be to end this fucked endless cycle by the goddess and start a new era of humans and demons side by side with every girl in the game in his harem including Erin (which Ceci will have to accept).