The 4th of December is
'Creating a Future Brimming with Love by Proposing' Day!
A commemorative day established on this date by a jewelry company because of the pun with 'Being happy together forever'!
The pun:
Forever → itsumo → itsu(mo) → itsu(1)
Together → the two of us → futari(2)
Happiness → shiawase → shi(awase) → shi(4)If you have the same feelings in 10 years...I'll think about itThere's a chance!