I think this refers to Su-Cool, in which characters are very "cool" in their composure, never panicking, and very straight-forward about things; other side soft, and sensitive. It's not the same as stoic, because of the straightforward conjecture created.
I find this funny... Reimu included... since in many things she's shown as a rather cold no nonsense girl. And I can see the other three being as such. (Flan-chan's so cute in this guy's style... never minding the fact she's crazy)
I'm starting to suspect that most of the "dere" types are more wishful thinking, fans tying themselves to a mental knot in order to interpret callousness as affection somehow.
Cooldere especially is 99% likely to be made-up, since it effectively translates to "affection that never shows". It's like a zen riddle - how do you know it's there if it never shows?
Marisa… I made a bit too much, so…Marisa~LunchMarisa, did you go and eat all my teacakes again? Go buy some more.Let's play danmaku until you break ♪You can stay here as long as you're quiet.I…it's not like I made it for you or anything, you know!Back again, are you?I have nothing of the sort!CoolKuudereYandereTsundereWhat? Where's your dere?!