Oops, it doesn't look like 'mikan day' is a national day..

Other days

fiancee

Fiancee Day
self care

Self Care Day
slime

Slime Day
first love

First Love Day
artists

Artists Day
pampering

Pampering Day
pick me

Pick Me Day
bounce

Bounce Day
ask out your crush

Ask Out Your Crush Day
nail polish

Nail Polish Day