I have a theory.
SPOILERS!!!
There's probably a fifth secret ending or more, i don't know yet. But i think that the MC did it, they seem to be the only one who doesn't get sacrifice and some of the options seems like the MC is lying or doesn't really care at all.
Like when everyone felt a chill down their spine, there is two options where you did feel it or not, that felt particularly off. Also the fact that no one seems to question if the MC did it and the only time where we get to learn about the MC relationship with Reina it gets dismissed by the MC themselves.
Each sacrificial ending doesn't bring back Reina, it was either due to the fact that they ran out of time or that the MC did it.
Maybe typing in a certain character name will get another ending? (Thought it was funny...)