Sesshomaru was on a murderous rampage after his dear baby brother who was trying his best not to be seen. By anyone. For he was embarrassed. Sesshomaru was on a rampage because he was going to be a laughing stock of the demons once the disgrace got out. Not to mention he was somewhat vain. But he was after Inuyasha because it was all his fault that he, The Demon Lord had been disgraced in the first place. For Sesshomaru's hair was pink. Noticable pink. His kimono was also tinted pink but not as badly as his hair. Inuyasha was also having a bad hair day. But his hair was so light a pink that you didn't even notice it. His kimono was the problem. It was also a bright pink colour that matched Sesshomaru's hair.
How it all began? Well some time ago, Sesshomaru had stolen Kagome's hair straightener. At least that is what he told everyone. In reality he had taken it as a bribe not to fight with Inuyasha while he was injured. He had run into Kagome in the woods on the way to challenge his brother (he had left Jaken, Rin and Ah Un far behind when he took off running way back on the plains) and she had stopped him anticipating his actions. She had pleaded in many ways for Sesshomaru to go away but nothing seemed to work until she pointed out what running so fast had done to his hair. It had gone all frizzy and windswept from being blown around. At this point Sesshomaru started muttering about knots and basically about the hundreds of bad hair days that would come of this frizziness. Kagome got an idea and fished around in her giant backpack for the straightener she had brought with her but never used and offered it to Sesshomaru. She pointed out the instructions on the back, told him what it was for and ordered Sesshomaru not to go anywhere near Inuyasha until he was better.
And this is how Sesshomaru got his hands on hair straightener.
Unfortunately Sesshomaru didn't read the instructions properly about how often to use the straightener and had ended up with straight hair that was like a white shirt in with never before washed colour clothing. Highly susceptible when washed incorrectly.
Many months later Inuyasha's group met up with Sesshomaru in an area covered in many hot springs. The area was filled with steam and was very warm. Sesshomaru was here to enjoy the hot springs originally (or let Rin enjoy them) but getting to enjoy beating up his younger brother was also a bonus.
They started fighting quite predictably and Sesshomaru in the beginning had the upper hand. Until Inuyasha decided to flying tackle him. They both landed in a spring and started fighting in the water making it the very image of a washing machine on high with the hot water making it very difficult to hold one's breath and both demons continually fighting each other to get to the surface for air. While the two were making a washing maching like action, the colour from Inuyasha's kimono ran and dyed Sesshomaru's hair pink while leaving the kimono pink too. For Inuyasha's kimono had never been washed in water properly like this.
Sesshomaru saw his reflection in the water and directed a 'you're going to die in three seconds. THREE!' look at Inuyasha who was busy freaking out about his now pink kimono.
And so the demon lord ended up chasing Inuyasha, claws out, electric whip and giant sword in one hand alternately and the half demon ended up running for his life from his maniac of a brother while trying to avoid being seen by anyone who could potentially mock his now pink kimono.