There are no endings where Ren kills anyone. There are "Dead Ends" (which you can get by making certain choices), but nobody dies or gets killed. Ren just restarts the day to give the player a second chance.
It's also possible for certain characters to die; however, their deaths happen off-screen, and it's not explicitly stated whether Ren was the one who killed them. They're also not endings.
You might also be thinking of the alleyway scene in Day 5; however, it's not an ending. It can only be unlocked by going down the "Decay" route.
Spoilers on how to unlock it: you'll need to pick all the indignant and dismissive options during Days 1-5 (basically... be mean to all the characters lmao), then dismiss Ren at the beach during Day 5. This isn't necessary, but if you want to guarantee getting the alleyway scene, I'd also suggest encouraging Ren's dark behaviour and showing interest in them whenever possible.