Some years before the Rukia incident.
“It was a dark night. I could see the world outside, but I always wondered what it is like. What it is like to be in the real world.”
During an attack on Soul Society- “You take cover, there is hollow behind you”. “Oh really, and I though that you already killed him”. “Don’t be a fool, move it.” Just in the last second, he dodged the cero of the hollow.
“You know, that was dangerous” “I know! That is why the ladies love me”
“Yeah, right…heh. Well we better finish the rest, before that so called Shinigami research team arrives”
“Aw, man and I just started having fun. Well then, later holly.” He jumped and kicked hard hollow in the face, breaking his mask off.
“Whoa, this was a close one. Well anyway, have you…” An applause is heard from the background. “Bravo,bravo. That was good one.”
“You are…12th squad captain, Kurotsuchi Mayuri”. He backed a little bit. Mayuri was standing with his vice-captain Nemu, and other Shinigami from 12th squad.
“Well, hello there captain. As you can see, we already finished most of the work, so you can without caring go back to your…” Mayuri just looked to him with a strong look.
“Silence monkey. You nothing but a experiment. Hmm, but as you said, you did right. Maybe I should send you to another experiment fight.”
“Wait…how did you just called me”. Another warrior stepped and front of him and said to Mayuri: “ What are your orders captain?”
“Hmm, well there are still hollow attack heard just outside of Seretei. You need to go and investigate that and kill any hollow you encounter. There is rumored to be even, Gillian class hollow,he he. But if you succeed, I will take in consideration about you departure to real world.”
“Thank you captain, we will see to it. Come on, we go.” -He takes him by the arm, and tries to move him.
“Just wait a minute. He promised us that he will name us successful and send us to the real word on mission. And I always wanted to see those nice school girls with their uniforms. So what is the problem.”
“You and your thoughts, if captain hear you, he will abort us. Now let us go and finish this.”
“FINE! But don’t you think it will be a little hard against those Gillians.” (they are moving fast to the west side of the border of Seretei)
“Well as the reports say, they can be a little tricky, but let us hope that they won’t come at us in large groups.”
“You said, but I actually hope that I will kick some more of them so I can show my courage to the women there in…” (Just in middle of their talking, there is heard a strange noise in the trees.)
“Wait a minute, I will go and check it out.”
“Wait a minute, I am going with you.”
“No, you stay here, just for if my illusion skills fail, we need your strong legs so they run and inform the situation.”
“Ha ha, fine then I will stay here. Like I wanted to come with you anyway.”
“ Okay then , I am off.” He jumped to the trees and began moving deeper.
“ I wonder what is there. Maybe there some nice girls, and he will be the only one to have fun. No fair at all, I am coming too.” But just as he approached, a scream could he heard.
“Wait, I am coming.” Then he was attacked by the masked ninjas.
“Wait, you are from the 2nd squad. What do you want.”
“ Silence monkey, you have no right to speak.” Then from the shadow, Mayuri approached.
“You, what did you do to him.” He was taking the battle stance.
“As I said, you were the failed experiment. Unfortunately I had him disposed, and I will do the same to you all. Created to hold the balance between the Shinigami and Hollows, and to fight along side Shinigami was your task. But you were not very good researched and so it ends here, little experiment.” Mayuri began drawing his sword. “Rip, Ashisogi Jizō.”
He then did shunpo and attacked and injured both his legs.
“Wait, what is this, I can’t move.”
“Hehe, as you may not know, abilities of my Zanpaktou are to paralyze your parts of the body that I stab. Of course, even if they are paralyzed, the pain is still there.”
“ You, you will regret this.” At the moment he is kicked in the head and falls unconcious.“
“ I am sorry little one, because I too put a lot of time into the likes of you.”
During the extermination this was one of the lucky survivors, who made his way, up to the market and eventually his real world.

Several years later at Urahara’s shop. “Hey, Ururu, could you please move the new delivered soul candies there in the corner. But it is described as the poor merchandise. Ah well then, just ,leave it there. I will throw it away eventually.”

But did he and what really happened to it. Well that is up to you to find out.