I wonder if he's running off to present to his father, since it says he'll only go and meet the vtuber after he presents it first. He abstained from reaching out even before he found out he wasn't biologically related, but the nature vs nurture discussion in this chapter and the prior thought that he could "prove" himself by writing well will probably give him the courage to reach out.
Edit: I wonder who the vtuber is. He said he doesn't recognize the voice, but assuming it's not a voice changer, that rules out the middle school teacher. He's already asked several of the more prominent female staff we usually see. Unless it's a no-name character, Imamura might be the most likely if they play up the gag of her inability to talk normally (in public) as a justification for him not recognizing her voice. She also works closely with Shirai, is one of the youngest members (aka a demographic more stereotypically in-tune with vtubers), and it would allow for a fun conclusion to the arc.
He hasn't asked Nashihara, Koike, or one or two of the other female staff, but they don't appear that often... He talks with Miyabe too much, and there's no way it's the brat.