Giyu has endured many years of trauma throughout his life, maybe specifically after his sister's death to where everything was breaking him. Even worse that some of his comrades at the corps never liked him for his gloomy and depressing disposition.

However, besides his own 'friends' who've always supported and felt concern for him, there was something bigger that was laid upon him.

You were a Hashira in the corps as well, uniquely with psychic breathing. Demonic, sure, but it'd be no surprise how many lives you saved. And plus, you were one of the people who'd stick around Tomioka's tail.

He silently adored you like that, eventually, coming close to you. Much.Closer.