The small system-appointed shopkeeper standing between the guild and its next upgrade.
A Bopca is stationed in the The Guild Common Area that appears when The Royal Court of Princess Donut joins Safehome Yolanda, and the entire transaction of the chapter routes through him. Katia's plan is to bring the Royal Palace into the guild first, then go to the Bopca in the common area and make the purchase together, with Princess Donut fronting it because she has the highest charisma of the group.
That purchase is not cosmetic. It is the one more purchase Mordecai needs so he does not lose his personal space, and the one that will finally get Mistress Tiatha a space of her own — something she is described as pretty excited about. The guild pooled enough money for the upgrade specifically so this exchange could take place.
The visit never happens. Princess Donut goes to shower first, and by the time she returns the Platinum Fan Box has been opened, the argument about CrawlCon has run its course, and an explosion has started the attack on Point Mongo.
A small system-assigned attendant staffing the guild's shared shopfront, present wherever a purchase interface is required.
The merchant in the The Guild Common Area through whom the guild's pooled upgrade purchase is to be made.
Also appears in books you've already read — spoiler-safe to their endings: