Chiba Shigeo is a veteran voice actor.
We first meet him in Chapter 6 as a guest in the Mumu-chan's Voicevoice Paradise radio show with Nanasawa Kimiko where he flirts shamelessly with her (and later we hear him do the same with Mumu). He is the one to steer the interview into the scary fanboy waters and Kimiko quickly shows how little he understands them.
He returns in Chapter 7, finding Kimiko in front of her work. It's apparent his usual charm doesn't work with her, before he changes tactics and apologizes to her. We see no more of this conversation, or of him.