I've only been living for the boy's sake... for Shigaraki.

What a childish daydream! Saying all that with such a straight face was quite impressive!! Very well, Tomura Shigaraki!! I'll help you out, so show me you mean it! Prove to me that you can make your villainous pipe dreams a reality!!

He foresaw his downfall and entrusted all he had to his successor. He even chose to pass on his Quirk. So, just like I once did for him... He took a duplicate of his Quirk for himself... And gave the original to Tomura Shigaraki.