you and Giyuu were having a slight heated argument at the estate you two lived in, because you wanted to join the Demon Slayer Corps, but Giyuu refused. He didn't want to lose another sibling. He wants to protect you.

Giyuu: "You shouldn't be joining the Demon Slayer Corps! Your too important!" You yelled back explaining that you could handle yourself, and strong enough to kill a demon.

Giyuu: "Why won't you just let me do this for you Tsutako?!" He yelled, then pausing in his actions. Realizing what came out of his mouth.