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

Other days

boyfriend

Boyfriend Day
one

One Day
lisp

Lisp Day
kiss a ginger

Kiss A Ginger Day
stud

Stud Day
ask out your crush

Ask Out Your Crush Day
bubble bath

Bubble Bath Day
tell a fairytale

Tell A Fairytale Day
gum

Gum Day
singles

Singles Day