Mc is a automaton fanatic think 2b from Neir
Mc has a system
Mc is reincarnated
Dxd is the base world
Our Mc Mai gets the typical truck-kun treatment but is reincarnated instead her body was too badly damaged to Isakei she doesn't get her memories back until she is 6 and a note appears after she gets them to explain why she was reincarnated. After a week of adjusting to her memories her system appears since Mai was an automaton fanatic her system is an automaton creation type. She can make other media characters into automaton examples Morgana Le Fay from fate or Momo from Mha or even Natasha Romanoff. Her system will help with blueprints for the body and a general outline for the code but it will provide the memories of the characters and their powers though the characters will now they are automaton but are in fact "real" if that makes sense. Once she figures out her base world the system has to inform her that it's a crossover world though not of what type of crossover so like sailor moon and Ranma 1/2 the crossover has to be something with powers mainly featured in it no purely slice of life. Mai has to make a few automaton of DxD characters to mess with people.