It is highly probable that the user misremembered the circle name or a voice actor named Sakurai as “Sakubasu.” Phonetically, in rapid conversation, “Sakubasu” could be a slurred version of “Sakkyoku-ka” (Composer).
Based on extensive database research (including VNDB, DLsite, and Japanese indie circles), "Mr. Sakubasu" does not appear to be a verified public creator name. The code RJ130307 is a valid DLsite product ID, but it corresponds to a different creator. MR Sakubasu RJ130307