[Shima may or may not have picked up or have worked on picking up more breaking in skills, but he's a spy not a thief, you know... Regardless, he is absolutely the sort of person who would try a door to see if it's open even if he hasn't been invited yet.]

...Oi, Okumura-kun...! I let myself in. [Calling that from the doorway before he wanders in, sleeve over his nose for now while he's trying to determine how sick Rin actually is. He pokes his head through the bedroom doorway when he spots that messy head of hair.]

How'd ya even manage ta get sick? Don't tell me it's that thing going around...