One option for that is that “kun” is a Japanese honorific used for amongst friends. Almost always for boys.
So you might call a friend Reedk-kun instead of Reedk-san, -san being more formal.
There are others -”sama” is more formal then -”san”, “-chan” or “-chi” is often used for small children.
My daughters name is xxxxko but we call here xxxxchi or xxxxchan - it stuck as a nickname after she grew up and I actually got in trouble with a Japanese teacher once for using it.
(as an aside ko means child and is very common ending for female names in Japan - my wife and both my daughters end in it)
ohmygosh - I just realized.
8-chan where chan is used for children
vs
8-kun where kun is most often used for teenagers and young men.
8-chan has grown up!