Artist's website gives reading as "おしょうすい".
https://www.pixiv.net/users/204966
https://www.pixiv.net/stacc/normad1017
https://pawoo.net/@osyousui
https://pawoo.net/web/accounts/1266
https://pawoo.net/web/accounts/4987
https://sketch.pixiv.net/@normad1017
https://mstdn.jp/@osyousui
http://steamcommunity.com/id/sahasa/
https://twitter.com/kousuke200
https://twitter.com/osyousui
