I’ve thought a lot about this, honestly. At first I didn’t think anything of Oboro other than a shady individual character who was very strong and had a lot of merit. He wasn’t very developed since we didn’t know much about him and he’s still really pretty shady.
The theory of him being Gintoki’s dad is one I can’t dispute or confirm, not with the information we have. We don’t know his age, his orientation, we don’t know enough about him to say if he has any relation to Gintoki. Obviously it’s the somewhat permy silver hair that makes him remind us of Gintoki and he does look older, maybe because of the darker circles beneath his eyes. I don’t really believe right now that Oboro is Gintoki’s father, but I also can’t say that it’s impossible.
Hair aside, there are a lot of things that Oboro and Gintoki have in common. They’re both dominantly right handed, which wouldn’t be such a big deal if they both weren’t so significantly dominant. Something to take note of, too, is how shocked Sada Sada was that Gintoki was able to hold his own against Oboro. That suggests that until Gintoki, there wasn’t anyone that held so much as a flame to Oboro’s fire.
The latest arc brings forth some questions for me. Like, it’s pretty heavily implied that Oboro was ordered to get rid of the Joui resistance and if he had Katsura, Takasugi, and Gintoki there, why not just kill them? It’s true he could have thought that having Gintoki kill Shouyo would be enough to kill their will to fight, but wouldn’t it have just been simpler to kill them all? Why spare any of them? If you look at this from the standpoint of Oboro being Gintoki’s father and him knowing that Gintoki is his son, then you’d see a guy doing what he can, in a really fucked up way, to find a way to spare his, possibly, only child. It could also be seen as a guy punishing his son for taking on another man as a father figure while also eliminating said adopted father figure out of the picture under the guise of orders. That is entirely speculation and there really isn’t much to back it up, but it’s a possibility. Plus, it’s also under the assumption that, if Oboro really is Gintoki’s father, he knows he is.
We don’t know where Gintoki came from, we have no fucking clue where he was before Shouyo found him. He could have been abandoned, he could have run away from home because living conditions weren’t good, he could have had his mother die and he had no father and nowhere to go so he was forced to leave — there are a lot of things that could have led to Gintoki being where he was when Shouyo found him. It could fit that Oboro knocked a woman up and left her not knowing she was pregnant and would later have his son. It could fit that Oboro wasn’t always such a cold hearted killer and loved a woman and it could fit that that woman died giving birth to Gintoki and it poisoned Oboro with hate and resentment toward a child that he either abandoned or abused enough into running away. There are a lot of scenarios that could fit the theory of Oboro being Gintoki’s father. Like, say, Oboro did love Gintoki’s mother and she died because of Gintoki, it’d make some form of sense why Oboro would later put Gintoki in a position where he’s forced to kill the person that means the most to him — Shouyo. That’s, again, just an idea, but it’s plausible.
Then, there’s the fact that Oboro refers to Gintoki as a demon. We do know they fought in the war, but was just fighting against Gintoki enough to merit the nickname demon or is there another reason for this chosen name? He also calls Gintoki a demon that howls at the heavens while Oboro himself is mentioned as a messenger of the heavens. These are things to think about.
Also, if Oboro is Gintoki’s father, then he’s the literal worst parent ever. Just throwing this out there. Worse than Hohenheim and Ging. The literal worst dad in the history of anime/manga dads.
And I will say that Oboro being Gintoki’s dad would be an interesting way to prolong the series. I’m not saying the end of Gintama is on the horizon or anything and I know Sorachi wouldn’t pull any cheap shots to prolong for more money or anything, but when this arc ends, the manga will likely do what it normally does after a serious arc and go back to the regularly scheduled mini stories and stuff, staying away from serious things/plot for awhile. Sakamoto and Katsura still need to be addressed, madao still needs to find a job, and learning more about Gintoki and where he came from would be interesting. It isn’t exactly necessary information and doesn’t have to be relevant unless Sorachi decides for it to be and should he decide for it to be, something like Oboro being Gintoki’s father would be a sizable punch in the gut way to go.
I’m not scared of whatever Sorachi has in store, I’m excited and looking forward to it. Thing are grim right now and this arc has made me cry more than once, I’ve recently been so anxious for these chapter updates that my OCD is flaring up, but, and this is difficult to explain, I trust Sorachi. He’s brilliant and talented and I trust him with whatever he has in store. And I hope this is what you were looking for with an answer! I actually have a few more things to say about the possibility of Oboro being Gintoki’s dad, but I’ll leave it at this for now!