Disclaimer: I don't own Bleach or any of its characters.
Regrets
Genryuusai regretted not being there for his wife, children, grandchildren, previous Vice Captains and nameless others when they died. He wished he could have see them one last time.
Soi Fon regretted hating Yoruichi because she never hated Yoruichi in the first place, even though she told others that she did. She wished she could stop lying.
Gin regretted seeing Matsumoto's face, as a last reminder of everything that he was going to give up for Aizen and his ideals. He wished he could forget ever seeing her face.
Unohana regretted not being able to save the lives of countless people, watching them die before her very eyes. She wished she could hold them and bring life back into them.
Aizen didn't regret hurting his Vice Captain and using his subordinates to his heart's desire. He wished he could have seen their horrified faces when they found out.
Byakuya regretted not doing more for Hisana, because nothing could be worse than holding her cold, lifeless hand. He wished he could rewind time and do things right this time around.
Tousen regretted not going to her funeral; instead, he hunted down her husband and killed him for retribution. He wished he could have said goodbye to her for the final time.
Shunsui regretted standing by his parents' freshly dug graves, long after everyone else had gone after the funeral. He wished he could erase that sinking feeling settling in his stomach.
Komomura regretted leaving his family, too shamed to see them again for leaving them for an unreachable human world that he did reach. He wished he could apologize to them for his cowardice.
Hitsugaya regretted letting sweet, gentle Hinamori get her hands bloody for the sake of defending a man that never existed. He wished he could take her hands and wipe them clean.
Kenpachi regretted raising Yachiru in the color red, carelessly letting her bath in it until it was all she saw. He wished he could have given her another color to see.
Mayuri regretted making his beautiful, perfectly imperfect daughter Nemu the way she was. He wished he could break her one more time and fix her properly.
Ukitake regretted having this sickness, for it dragged him down, making others worry about him, and it was the last thing he wanted. He wished he could take it all away.