My otp:  Dojima and Adachi.  Because Dojima still treats him like his partner in the end, calling for a stretcher, and going to visit him while he’s in prison.  And I think Adachi actually felt bad for what he did, there’s something about the way he looks when the police are like, “His old partner called for a stretcher,” just… the entire time during the fight against him it seemed like he didn’t give two fucks, but then there’s this moment where I can feel him being like, “… oh god what have I done?”  Because Dojima (and Nanako) were hurt.  I actually believe that he DIDN’T want Nanako to get mixed in everything, that he sort of had this kind of blissful family experience with Dojima and Nanako.  And that, to me, made Adachi a really interesting character.  Going from dumb cop, to someone who just didn’t seem to care, then in the end there’s this hint of, “Actually… he cared for this one thing,” just gives him more meaning.
My most hated pairing:  Really don’t have one. 
My unusual otp:  I’ve seen some “shouldn’t be pretty” pictures of him and Souji (shouldn’t be pretty means that the picture shouldn’t be pretty because it’s wrong for whatever reason, but it’s pretty) but… I’m not sure if I can pair them together.  Like, Souji is obviously important, but… I dunno if I can cross that line.  But I can see how others can?  And do?  I think the strangest OTP I’ve had for Dojima is with Naoto.  Just… I’m not sure why he never addressed her being a child – she goes to school with Souji – and a woman and her issues.  I feel like he could have talked to her about things, and been like, a great mentor of sorts.  Whether it crosses into relationship territory is debatable, but again, it’s that whole “shouldn’t be pretty” thing. 
My crossover otp:  The only one I ever sort of had as a joke was Dojima and Matsuda from Death Note, but that’s because Matsuda reminded me of Adachi, you know, that young cop who kinda messes up sometimes?
My brotp/friendship otp:  Refer to previous answers about Souji and Naoto.  
Character headcanon:  Dojima really, truly cares for his family, even if it doesn’t seem like it.  I think after his wife died he was completely lost.  Think about it.  Losing his wife, he’s suddenly a single father to a very young child.  And he’s a detective, so there’s this sense of, “I have all of these resources, I should be able to figure this out right?”  I think Adachi became part of that family, like, he became more of a partner.  Whether you see that going into sexual territory or not is up to you.  But I sort of think that Adachi is that “optimistic” cop that Dojima was, once upon a time, before his wife died.  And Dojima needs that around.  So when it turns out that Adachi is the one behind everything, Dojima just sort of clings to the old times with Adachi, you know, the dumb cop he was, “Idiot probably needs a stretcher,” and things like that.

I also think that he sees himself in Naoto, you know, the young upstart who thinks they can come in and take on the world?  That’s why he’s not too hard on her (and why I wish they would’ve interacted a bit more, ESPECIALLY since he talks to her on the phone when Nanako is taken and she’s all, “Surely you knew the case wasn’t over yet!”)