Setsubun

February second is a day ofcalled "Setsubun" in Japan.

"A day of something" is not used for the names of traditional events or holidays. Eg: you would NOT say "December 25th is a day of Christmas", but you WOULD say "Christmas is a day of celebration." However, I think you probably don't call February 2nd "Setsubun", so i think perhaps an even better correction might be: On February second, an event called "Setsubun" is celebrated in Japan.

Setsubun celebrates the change from winter to spring, and people do amuleta protective ritual by throwing soybeans.

I'm going to guess "amulet ritual" is meant to mean a ritual that will protect you from something. Unfortunately, "amulet" is not an adjective.

This is because demons don't like soybeans, which isare a symbol of vitality.

Just a grammar mistake, plural words like soybeans, should us "are" instead of "is".

IfWhen children doare doing this spell, a man often wears a demon's mask, and the children throw beans at him.

I removed the "If children do this", because it sounds like you are saying, if the children do the spell, then that causes a man to put on a mask. "When" just means they happen at the same time.

After enjoying throwing soybeans, people eat as many beans as much as their age number.

February second2nd is a day ofknown as "Setsubun" in Japan.

SetsubunThis day celebrates the change from winter to spring, and people docelebrate it by performing an amulet ritual that is done by throwing soybeans.

This is because demons don't like soybeansSoybeans, which isare a symbol of vitality help ward off demons, who do not like soybeans.

I think it would be helpful to explain here to people who do not understand what Setsubun is what the demons represent in Japanese culture, just like how you said soybeans are a symbol of vitality.

There is also double meaning that The word “beans” in Japanese arealso has a double meaning; when pronounced ", it can also mean “destroying evils”."

The spell during thisThis ritual is performed with a spell that says, "Demons go outsidedemons out, happiness comes insidein."

I think the most natural way of saying this would be to omit “spell” and say, “While performing this ritual, people chant “demons out, happiness in”.

If children do thisIn the ritual, a man wears a demon's mask, and while children throw beans at him to ward off the evil.

After enjoying throwing the soybeans and having a fun time, people eat the number of beans as much asthat corresponds to their age number.