Given how PSO2 has its concerts, a collaboration with Hololive could be rather appropriate. They are advertised as idols (even though they probably crush Yagoo's dream every day) and many of them do sing. It wouldn't also be the first collab they have done either; Hololive had a collaboration with Azur Lane in the past.
https://www.youtube.com/watch?v=Pd22wbqeQDE
They have oversea fans as well, despite streaming in Japanese. A number of them have made the effort to try to learn English to communicate with more of their fans as well. They are also rising in popularity and hold some of the top Superchat earnings on Youtube.
https://www.youtube.com/watch?v=vLcDUQ7ziAM
Some other Hololive videos to look at:
- https://www.youtube.com/watch?v=9kQ2GtvDV3s
- https://www.youtube.com/watch?v=68KV7JnrvDo
- https://www.youtube.com/watch?v=WKmzvtEv9Wc
- https://www.youtube.com/watch?v=5yDNEmcKQFY
- https://www.youtube.com/watch?v=3cqV5BKJHyk
- https://www.youtube.com/watch?v=zLak0dxBKpM
- https://www.youtube.com/watch?v=iix0fCbyfZs
The official Hololive website: https://en.hololive.tv/