Our little aid project this time involves going around to each room and playing the role of the oni.

Oh, by the way, why do we throw beans at oni, of all things?

The beans (mame) in this case is derived from the word "exorcism"(mametsu). In other words we're exorcising evil spirits, so to speak.

Ooh...

Hey since we're going through the motions anyway, why don't we act as their fears instead so they can learn to get over those?

Good idea!

And since the oni is one of the better known examples of an 'evil spirit', they got chosen, I think.

ANGRY ONIIIII!! Onioko, alternative kanji reading of Kinu's name.

That's why it doesn't necessarily have to be an oni. They say that people with the word "Oni" in their family names would even say "In with the Oni!" instead of the usual "Out—". Well, at least Wikipedia says so.

TYPHOON Ryuujou was severely damaged by a typhoon.