These songs come with the Lunar New Year Campaign.
There are 3 songs on Aqours B-Side too!
It was pretty hidden but Wonderful Stories has come up alongside the current event (Although It should be playable after the event).
For anyone who hasn't noticed until now (like me): there are a few songs on µ's B-Sides (didn't check Aqours though) with 10x EXP BONUS.
Just got halfway through to my next rank up with only one 4x EX song with 3320 gained EXP.