gacha

Nasu: That's a tricky one. A minus sign is like that one thing, you know? It's like a B in terms of rank, but for your ability it's less than a B, maybe even a C. Something like that. Think of it as a number that's not very stable. Also, take care of your hair.
Takeuchi: I see. Kind of like when a new game you've been waiting for causes your writing speed to become unstable.
Nasu: A clear, perfect example, thank you... Please be gentle to mushrooms.

Now, things like B+ and A+ represent the unique ability to multiply these numerical values for just an instant.
In other words, an ability ranked B+ would normally be weaker than an ability ranked A, but can momentarily exceed it by doubling its own power from 40 to 80.