The software he uses is this game Honey Select which is technically a scene creator. Here's the English version with screenshots. But he could also be using sequel Honey Select 2.
Your question was clear... But so was the answer, I'm afraid.
If you would like it more technically worded:
- The 3d assets he used to design the characters are included in the game Honey Select (used with permission) - or possibly its marketplace.
- The tool he used to combine those assets, pose the characters, and export them into static images and animations is the game Honey Select.
- The ultimate source of the characters' *design* is Runey's own imagination - as limited by the assets available to him due to the toolset he is using.
I hope that answers the question, otherwise I am not sure what you are asking.
Worst case scenario, try asking in (I assume) French.
Sorry I am late, I rarely check notifications on here. I just wanted to add the assets he used were not permitted by Illusion, the developer of Honey Select, or there western retailer and publisher Fakku who released it under the name Honey Select: Unlimited. Here's the source: FAKKU Addresses Unauthorized Use of Honey Select Assets
It's not like anyone would report this game so it is safe.