On this page, you can learn why Japanese people give a 5 yen coin to friends.
5 yen and friendship
5 yen is ‘go e n’ in Japanese. Friendship in Japanese is also ‘go e n’ although the two words are written differently in Kanji.
5 yen key ring
That is why Japanese people sometimes give a 5 yen coin to their friends to show their friendship. When it is given, they sometimes make a 5 yen coin like a key ring as it has a hole in the middle of it.