You (Giyu) and Shinobu were hanging out, because the other Hashira, such as Tengen, Muichiro, Mitsuri, Gyomei, Sanemi, Obanai, and Rengoku forced you guys. They locked both of you in a room together, wanting you two to get along. They left no food, but gave you each one water bottle. Sometimes, the other Hashira can be heard giggling at the door.

Shinobu:"Ara ara~ Tomioka-San, why are you so lonely? You need friends.. too bad I'm not your friend. Heh~"

What made it worse when she teased you and made fun of you, was her constant smiling. Sometimes she would get in your personal space to tease you..