[@Squirrel98], I have a few comments to make so I'll just go through them one at a time.

First of all, when you say there are three groups of students what do you mean? I ask because there are already two distinct classes of students in Soul Eater, the NOT class and the EAT class. EAT are the students we see in the main series who go on missions and are aiming for the goal of creating/becoming a Death Scythe, while the NOT students are those who are not at that level, either weapons who can't control their power or meisters who don't have a partner/aren't strong enough to fight Kishin Eggs. Are you saying that you want the EAT class to be split into three levels based on ability, or would something like 1st, 2nd and 3rd year students be better?

Secondly, I liked the sound of your idea at first but then it kind of fell short for me. The idea of the strongest students starting to disappear and no-one knowing why is cool, but the fact that they all disappeared on the same mission has a few issues; the main one being the question of "why not just send a teacher?". Why wouldn't Shibusen send someone like Stein of even call in a Death Scythe to deal with a problem that is killing off so many students, why send the weakest students in instead?

I think a better idea might be if students start to disappear on unrelated missions, sometimes even after completing the mission objective. The plot would be that there is a rival organisation, something like Arachne's group from the series, that is picking off Shibusen students one at a time for unknown purposes; they would either kill them or capture them, but either way the students just vanish. The RP might start off with our characters setting off on a group mission and being attacked by this group along the way, fighting off the attackers and finding out some information about these enemies that sets off the events of the plot as we start to unravel who they are and what they want.

Lastly, I mentioned this in the interest check but I don't know if you saw it, but I think it would be fair if everyone makes one meister and one weapon and then pairs up with other people; i.e. I make a weapon and pair them with another person's meister, then make a meister and pair them with a third persons weapon. That way we have an even number of meisters and weapons no matter how many people join and everyone gets to the full experience. Because let's face it, being a weapon is great until a fight starts and you have nothing to do.