Foster functions as the Wellacaster family butler, directly executing Carol Wellacaster's commands. His core duty involves training household maids to meet specific demands for entertaining the family's affluent business partners, acting as an enforcer of Carol's control over the staff.

Before Carol seized the estate through disputed means, Foster trained individuals known as "lust objects" under the previous owner, Dred. Following Carol's takeover, she forces Foster to resume this training under her regime.

His history with Clair Barton, the displaced heir now working as a maid, adds significant complexity. Their past interactions forged an emotional bond described as Clair's love for him. The resumption of his training duties under Carol's coercion directly strains this relationship, putting Clair's feelings for him to the test.