Benihime's cheerful and playful voice came ringing from the depths of Kisuke's soul, 'You rang~?'
'Based on your tone, it seems that you really know the reason.' Kisuke sighed.
'And you won't ask why I didn't tell you?'
'Because I didn't ask anything about it.'
'Right. And you're too busy with your other projects.' Kisuke can hear Benihime chuckling.
'So? What happened back then?'
'I just witness what happened so I'll just tell you that as I'm also not entirely sure about what exactly happened.'
From Benihime's words, it seems that she's already awake before Kisuke is even born and has been taking care of his injured soul due to 'transfer' ever since. Back then, the father figure of the Urahara Household is already missing but Benihime isn't really interested in that.
What caught her attention is Kisuke's mother, Sakura Urahara, has been using a strange technique she has never seen before on the baby in her womb. Benihime was, of course, very alarmed at what she's doing and safeguarded Kisuke's soul more. She planned to forcefully materialize herself if it's needed and wouldn't hesitate to do so as Kisuke only needs his soul to survive.
However, soon enough, she dropped her worries as the technique Sakura is using only affects Kisuke's physical body. In the duration that Sakura is changing Kisuke's physique, Benihime only watched carefully for the changes.
Since she's only an expert on soul composition, she isn't exactly sure what's happening on Kisuke's physical body nor Sakura's goal. Benihime, however, also has keen eyes so she can tell that a certain 'part' of Kisuke is being pushed towards his heart and from what's Kisuke is guessing, it's probably his 'Devil's Lineage'.
'Pushed to my heart? Then where is it now? Did it go out somewhere else?... No... As far as I know regarding the physical bodies of this word, it can't go anywhere. Although trapping or cornering a 'lineage' is theoretically possible, it shouldn't be possible for it to completely separate from the body. Else it'll be an incomplete body and it would breakdown sooner or later.'
'You're still forgetting something here. Remember, it is your heart.' Benihime soothing voice gave him another clue.
'Heart... heart... heart!?' Finally, Kisuke was able to piece the puzzle together and an idea that could explain what exactly happened flash in his mind, 'Could it be... the Hougyoku!?'
'Correct. That scary toy of yours took it.' Kisuke can hear Benihime chuckling again. She then continued her story.
Sakura managed to gather all of his 'Devil Lineage' in his heart before he is born and locked it in his heart. Benihime tried to inspect it but the lock is strong enough for her to not be able to mess easily so she just ignored it and continued nursing Kisuke's soul. She wants his soul to completely recover or at least, mostly before he's born in this strange world and she's successful in doing that.
However, a sudden change occurred when Kisuke is about to be born. The Hougyoku, which is has been inactive all this time after safekeeping Kisuke's soul through the interdimensional transfer, suddenly started devouring what's inside Kisuke's heart from the gate of his soul.
Benihime doesn't know what happened to that thing which is locked up but she can tell that Hougyoku's cracks worsen and the integration of Kisuke's soul to his physical body became a lot better.
'And that how it disappeared. I don't know if it's forever lost or the Hougyoku is only keeping it. Either way, the fact that this thing could do something without anyone's consent is scary. I can understand your reluctance to use something like this that has a will but no intent.'
Benihime is correct. Kisuke didn't want to use the Hougyoku as it can initiate actions regardless of the user's will or intention so he can only seal it in the middle of his soul so that it wouldn't affect him if it moves on its own.
He already saw an example of it in the past when Aizen's Hougyoku suddenly stopped supporting him and Ichigo was able to weaken him sufficiently that Kisuke was able to seal him. Though Aizen is still pretty much a monster due to the raw Reiatsu that he possesses that is probably only lower than that of the Soul King which holds the worlds together.
Another reason why he didn't want to touch the Hougyoku after his initial use of breaking down the barrier between his Shinigami part and the Hollow part is that there is really no real use for it. It's true that he can gain unimaginable power in using it, but he has other options to get stronger without the risks of the Hougyoku brings.
But now that he knows that the Hougyoku is holding onto his 'Devil Lineage', he intends to make room in his schedule to search for it.
'And what happened after that?' Kisuke decided to push it into the corner of his mind for now and hear the rest of the story from Benihime.
'After that, nothing really happened much, but your mother seems to be very surprised at the fact that you're completely human. From what I can tell in those times, it seems she's very knowledgable regarding physical bodies or else it would be impossible for her to push that into your heart and successfully lock it. She could have examined your body with much more precision and accuracy but I guess she doesn't want to do that to her child. You really got lucky in this life.'
Kisuke smiled gently while remembering how his mother took care of him, 'I'm really lucky... And I'm thankful... But after this revelation, things got a lot more complicated and I have to make a few security measures.'
'Oh right... The thing we talked about last time. How is the progress of that?'
'Not great. I need a lot more data to actually make a working prototype.'
'Then that's not good. You already revealed yourself and more annoying things will be coming, not just for you but also for those around you.'
'I know... But there are also advantages of revealing myself. Now can also get the attention of those who can help me. Besides, I technically saved the heiresses of large Devil Households so I can ask a few things. That way, my research can progress.'
'That's true... Then I'll be waiting for that time. But let me warn you. You would have to separate me from your Hollow side at that time. It'll result in more violent reactions if you use it.'
'I know. It'll also be a good time for me to actually control it, so it's not really a bad thing.'
Kisuke and Benihime finished their conversation. Instead of returning to reality, however, Kisuke kept thinking of the possibilities and the paths he could take. Sorting out his priorities in his head, he decided for his next course of action, 'Safety first. I have to finish Benihime's thing first before anything else.'
As he's running simulations in his head, he suddenly felt someone pulling his right ear which dragged him back to reality, "Eh?"
"You brat... It seems that you're already somehow aware of our relationship and escaped to your own world. You still have a lot of explaining to do." Sakura is looking down on his troublesome son who seems to be already planning something else. She noticed that Kisuke is the only person in the room who isn't affected by what just happened.