Board Thread:General Discussion/@comment-24882930-20160331125812/@comment-9552368-20160401120216

I like how Yachiru is the spirit of the sword of kenpachi. Think about it. All the people as we saw so far gets Bankai because they must talk to the sword and try to get along with the spirit inside. Most people doesn't get bankai because of that and the ones that get it it's because they force the spirit to accept themselfs.

But you know. The sword is part of yourself and as such it wants just 2 things: To accept it as a part of your personality and that it cares about you because it's a little too much egocentric (well, it's part of you, so you are his priority). And what do almost everyone? Use his powers for others. That's why most swords doesn't get along with his user because it want to use the power for both of them and not for others.

Now check Kenpachi. Why do you think Yachiru liked Ken so much that it materialized? Because Kenpachi it's the only one that fight just because he likes it. No "I will save XXX" or "I will do it because it's the right thing". His sword was all like: WOW he does what he wants to be happy even if others don't like it. I like that, it makes me happy, it makes US happy".

She needed to materialize because he liked so much Kenpachi that she wanted to help him and she couldn't just use his true powers because he was refusing to use all the power after the batlle with Unohana.