The song is Vocaloid's "Just a Game" (lyrics and composition by takamatt) sung by Yukina Kita（北如来那）.
https://www.nicovideo.jp/watch/sm1474...
Original song
https://www.nicovideo.jp/watch/sm1093...
Yukina Kita's homepage
https://kitayukina.com/
Video List of Yukina Kita
   / @yukinakita  

My video list
https://www.youtube.com/@noho91/videos
My woodworking homepage　（のほほん木工房）
http://noho91.web.fc2.com/