This is my take on what Hichigo/Shirosaki/Hollow Ichigo must be thinking while stuck in Ichigo's head. Can be HichixIchi if you pass it through a magnifying glass and squint and also if you want it to be its totally your choice.
Disclaimer: Tite Kubo owns Bleach. I, on the other hand owns only the plot of this story.
He always acted the same. Ever since he can remember when he woke up to the world of sideways buildings and clouds with the endless rain. As far as he can tell from his questionable existence, he was there for the boy or rather, made for the boy. At first he couldn't comprehend why he has to be there, after all, the boy already got the old man to guide him in his bleak and dreary world. So he continued to exist without his existence being recognized. Of course the old man knows he is there but that barely even counts. So he stayed in the shadows because he doesn't actually have a lot of choice. That is until he was called upon to help the carrot top out. Something to do with one thing or another. Either way he is glad for he finally get the chance to discover his purpose for existing within the boy's soul. His appearance came as a shock even to him, I mean it's not like he can actually see that the color of his skin is white in the dark and when he caught a glimpse of his eyes on the window in one of those sideway buildings, all he can do is shrug and he briefly wondered if molten gold in a sea of inky black is normal. And surprise, surprise it's not. Not his skin, not his eyes, not even his whole damn existence as he quickly learned. It's so damn frustrating to be able to walk, talk and even think in his own and make judgment calls as he goes but not being able to be considered as his own person so he fought. He fought the boy and taunt and leer and make fun of him to hit him where it hurts just so he could vent out his confusion and frustration to him. He knows it's not fair but hey, the world is hardly ever fair. So he continued to act the way he does, infuriating and pushing the strawberry to his limit so he wouldn't have to deal with his own vexation. But like every battle, it always end with someone standing on top of the other and that means he is generally kicked in the butt by the hero infested complex boy. But that didn't mean he just take it there sitting on his ass because in every one of their fight he almost, the key word almost, win until some random burst of determination course through the others soul and beat the shit out of him. Every. Fucking. Time. And that's when he started to call him King. And that's when he also realized that if he could hand King his ass in a silver platter maybe he could take over and be the King and be in control for once. For he never had the joy to experience being the one in control except for those miniscule amount of time that King slips up and unwittingly give him the reins of his own but it is always short-lived. So with that in mind, he began harassing carrot top with every opportunity he gets. And it's fun, for awhile. Because then he started to unexpectedly become King's enemy to the point that King wanted to erase his existence permanently So King seek the help of strangers to get rid of him. And so the fought. This time one of them shall be King and one shall perish. And he lost. Again. Like all their other battle. He was sent to oblivion indefinitely and King hoped, permanently.
But he awoke once again, under dire circumstances of life and death situation (since when did King is never on a life or death situation?). And he was in control, but not really because he was still confuse as to what is happening so he goes with his instinct (one of his abilities that he is sure he can rely on).
The next time he awoke is from the feeling of him being dragged out to from darkness. And when he was out, he was informed by the younger version of the old man that King wanted them to be one. And so they did. Towards the end of it, they all know they will all perish. But it is such a steeply high price to pay. But then again, he is not the King so he made peace with it. And if ever wake again he just hope that it will be in better situation (but who was he kidding?) and he will fight for control against King and continue his questionable existence.