Ingenuous, pronounced in-gen/jen-you-us, is an adjective that means "(of a person or action) innocent and unsuspecting." Synonyms include naive, innocent, simple, childlike, trusting, and trustful.

Disingenuous is also an adjective, and it means "not candid or sincere, typically by pretending that one knows less about something than one really does." Synonyms include dishonest, deceitful, and underhand(ed).

Katsuki is not ingenuous, but he's not disingenuous either.

Deku, on the other hand... (squeezes him and squeals) IS ADORABLE AND INGENUOUS!!

Tomura: (raises hand) I'm disingenuous!! And so is my Master; I learned it from him!