Here how it would be my idea for the Demon Slayer DxD original. I wanted to be a crossover like those based on a highly well know story plus an additional series that is thrown in the mix. I was goijng to have Hero Academia DxD which is the most popular My Hero Academia x High School DxD story but the twist is that Tanjiro is sent there and he would be the main character. If you don't know what is the deal with Hero Academia DxD here are some point notes, Izuku is Issei, Ibara from 1-B is Asia and Momo Yayorozu is Akeno. Not fully manifested but they get similar things, also Izuku gets an harem that is really unlikely even for the standards.
Now how would Tanjiro factor into this, well he would be brought into the hero world or ''the future'' the same way it is the same story, but he would bump into Rias early and she would just think he is just some random kid. He would meet Anya and the whole thing, while Tanjiro is trying to see what to do while stuck in this world Izuku is having his adventures while Tanjiro is trying to fight his way back.
Things would happen, like he meet Sona and the others, he goes to visit UA and gets interested in the hero course and it would be a battle to see who would get each girl. Like Rias would be torn if she wanted Izuku or Tanjiro. I won't go into more detailed because it would spoil things of my regular series.
I hope you all see why I decided to drop this off and go on a different direction. Tanjiro is one of my favorite MCs, he is good, honesty and he didn't had the whole ''you were chosen'' bullshit. The author even tried to tease that but she was smart and told it wasn't true, Tanjiro really worked his ass off. Well, I hope to see you all next chapter.