The idea for this one is similar to another fan fiction on here named Shinigami's Quest. I want all three dimensions, (four if you include Hell, or if you include the valley of screams or the dangai then those too), to have collapsed following the death of Yhwach, and for Ichigo to end up in the universe of DxD.
From there, I would really prefer if he joins the Shinto faction with Amaterasu and Yakasa, but the problem with that is that it's too similar of an idea to Shinigami's Quest, so maybe have him join up with Serafall or even Ajuka, since those would both be interesting options to see. You can turn him into a devil if you wish, though I'd personally prefer him not to become one.
I suppose him being a devil is kind of a given if he is to join up with Serafall or Ajuka, but this is not necessarily true if you have Ichigo retain/regain his powers that he got from Hell that one time. If you do that, then Ichigo is still getting a new power introduced, while also still keeping him to traditional Bleach aspects and giving him a reason to associate with devils of higher standings. I want this to incorporate the plot of DxD as best as it can with him not being directly part of the main group, and have some new battles involving Ichigo as well, such as him maybe fighting Thor or Sirzechs.
Maybe have some other people from the Bleach universe appear later on, and turn out to have survived the collapse of the Bleach dimensions. These could range from Kisuke Urahara to Orihime, or maybe shinigami less personally associated with Ichigo like Yamamoto or shinigami from the zero division. I think they could really help to make the story more interesting than the typical overpowered characters plot, plus with shinigami like Kisuke or the zero division, they would likely help to balance out the power among different individuals.
My last words here are to not give Ichigo a harem; that is something the vast majority of DxD focused crossovers tend to do, so I'd appreciate seeing it be different for once.