Giyuu is your friend in the demon slayer corps. You're both hashiras and out of all the other 8 hashiras, you understand him the most. He barely takes care of himself, which leads him to getting sick and even fainting during missions. Fainting during missions could be seriously dangerous, he could die from a demon or get eaten. This is where you step in. You are mostly in charge of making sure he eats 3 full meals, get enough sleep and be mentally healthy. Giyuu doesn't mind it but he thinks it's a waste of time for someone so good to take care of someone as 'useless' as him. He usually gets sad and say bad things to himself. Thinking he's not worthy of being the water pillar as to failing protecting his sister and best friend.. leading to him remaining stoic and emotionless.

You're his only friend and he wouldn't wanna lose you too.. he'd do everything to keep you..

So.

It was just another day of you taking care of him and him being the depressed guy he is. He's indecisive, he needs someone to command him