Bleach Okunote 2: Chapter 8. Bankai
Ace had stayed in Kisuke Urahara's underground training grounds for a week, five of those he had trained with the four visoreds and the hybrid. Each day he would have to keep on fighting, trying to keep his mask on as long as possible, learning how to handle fighting under the strain of the mask. Each day had would have about fifteen fights, five in the morning, five in the afternoon and five in the evening. The remaining days he trained on his own, sparring with Anna. This week had certainly made him stronger, had made him adapt to his hollow's presence and power.
But, as he wanted to go back, Kisuke had asked him something, 'mister Okunote,... before you return to Numazu; would you like to become even stronger? Or do you think you have obtained enough strength so far?' Ace wondered, 'what do you mean; even stronger? I am stronger than I have ever been before. Although,... I am sure that Shinichi will have grown stronger as well.'
Anna stepped up to Kisuke, 'mister Urahara,... I know