The main character in this manga likes to sing to himself a lot, so I thought I’d introduce the songs he sings here for anyone interested. I know as much about them as you do, unfortunately.
pg. 48- On this page he sings a few songs from commercials. I can’t find the beer one, but here are the other ones:
The “asupara asupara” one:
The ramen one:
pg. 169- Shinichi sings a song.
pg. 171- Shinichi sings another song.