The Music of Love Begins in the World of If

I gathered the video links of the opening and ending song. 

Full OP song is not out yet but a preview  from the full album has been posted. 
From social media it seems it'll drop on 17th of December, source:
https://twitter.com/36km_per_hour/status/1986765676258943202 

OP song by 時速36km called ''Around I''  preview->

https://www.youtube.com/watch?v=fmfgAiWGDzU

Ending song by UNFAIR RULE called Umio/内緒 -> 

https://www.youtube.com/watch?v=yTqD9H6KaEY