Mitsuri, the Love Hashira, is one of the fan favourite Hashira. In her backstory, we learnt that she possess immense strength even as a child, easily overpowering even grown man. However, she found herself unable to find a suitor growing up. After her failed marriage negotiations, she realized that she has to hide her true self. She pretended to be weak, held back from eating and even dyed her hair pink in order to be more attractive. In the end, she joined the Demon Slayer Corps to fulfil her goal of finding a suitable husband who is stronger than her, rising to the ranks of a Hashira due to her physical prowess.
Correction
Um actually … She didn’t dye her hair pink. It became pink because she ate too much sakura mochi.
It was deemed abnormal and thus she dyed her hair black. (However, this doesn’t seem to occur in the manga, and was depicted in the anime)