← Youmu-chan, whose knees gave way and can't stand up← Just a meter without a particularly deep meaningwob—
A commemorative day established on this day because of the association between the way the word "knee" is pronounced in English and the fact that having no knee pain would make you smile!
The pun:
Knee → ni (pronunciation; 2)
Smile (as in, a gentle, pleased smile) → nikkori → ni(k)ko(ri) → ni(2) ko(→go; 5)—ble
