Grimmjow wasn't used to the concept of 'friendship'. He didn't really understand it, either. What kind of relationship was 'friendship', anyway? Didn't it mean you had to see someone as an equal? Not just in terms of skill, but in everything? He couldn't fathom that.
He wasn't 'friends' with his fraccion. They were weaker than him, both in body and mind. Weak cowards. He joked with them, and fought alongside them, but in the end they were subordinates, not equals. Not friends.
Kurosaki and the others made even less sense to him. Kurosaki was willing to die for any one of his 'friends'. He would throw himself in front of a Gran Rey Cero, would take all the hits Grimmjow would hit him with, just to protect his 'friends'. And the girl, the little princess. She was soft and quiet and easy to intimidate, but when he threatened Kurosaki she stood up to him and stood tall and firm, despite having seen what he could do.
Those people were hurting for each other and nearly dying for each other, and it just made no sense to him. Why? Why sacrifice yourself for someone else? All it gets you is dead.
And then Kurosaki nearly died for him. Jumped in front of Nnoitra's blade for him. And after trying to stop him from hurting himself, trying to convince him to stop fighting - even offering to fight him again.
It made no sense. Why would Kurosaki do that for him? He'd nearly killed the shinigami three times, threatened his princess, wounded his little ice queen…he'd hurt the boy's so called 'friends'. And yet Kurosaki still extended a hand, and still saved his life.
And of course, after that he'd had plenty of time to consider things. Eighteen months of loneliness is enough to alter one's priorities, really.
He began to feel like…it might be nice to have someone to be there for him. To talk to, no strings attached. Just someone to provide company. It was…comforting? To think about it. Someone to be there would be nice. Not feeling alone would be nice.
He didn't know if he could be there in return - how was he supposed to 'be a friend' when he didn't even completely understand the concept? But he figured he could try. He hadn't let not knowing how to do something stop him before.
The concept of a friend was foreign to him, but, he decided, it might be nice to have one. If it really was as good as it looked.
But as for the who…that of course was the hard part. But he'd heard a human saying once, 'good things come to those who wait'. Well, he hated being patient, and had scoffed at that stupid little saying. But…
Eighteen months was a long time, and among other things it had taught him patience - well, to a small degree. But he figured he could wait a little while longer, see what happened.
It's not like he'd know what to do, anyway. So let someone come to him.
