After talking about the Yu Yu Hakusho manga, I finally decided to just look at the stuff the anime left out.
170: Kurama tells Kuwabara about the Demon World Tournament, Yusuke returns after a year and a half, it's revealed that King Yama was corrupt and Koenma took down the barrier around the Demon World. Kuwabara's father appears, and he's become an ambassador for the demons. Yukina is an exchange demon, and will be living in their house.
171: Months later, demons are starting to integrate into society, and the Dark Tournament announcers have become popular idols. Yusuke has started a private spirit detective agency, with a ramen shop as a front. Keiko tells Yusuke about a strange incident in a girls dorm room, and Yusuke has to dress up as a girl to get in. Yusuke can't figure it out, so he has Kurama solve it for him (he's upset about the idea that he wouldn't have to wear a disguise to get in). They hire a demon to scare the actual culprit, one of the human roommates in the dorm room. Keiko doesn't pay Yusuke because he had Kurama solve it, so he tells her he sold her school uniform to a creepy old man for a high price; he actually just gave it to his mother. The moral is that humans are worse than demons, but in the last panel, Togashi's editor says, "Wait, isn't Yusuke a demon now?"
172: Stuff we saw in the final episode, with Hiei and Mukuro, and Mukuro's backstory, which the anime moved to a different part. There's a part I don't believe the anime adapted, with Hiei capturing the man that enslaved Mukuro with one of Kurama's plants, which immobilizes him and will prevent him from dying from torture until his head is cut off, and giving him to Mukuro as a birthday present.
173: A series of short stories with various side characters, including that one psychic with the rule-setting power playing video games with Gamemaster, checking in on the love lives of the Dark Tournament guys, and Botan and one of the other grim reapers getting food in Demon World with Koenma to cheer him up. This is where Yusuke's father shows up.
174: Koenma and Botan are taken hostage by demon cultists who don't like the new peace. They threaten to fire an interdimensional laser at the human world if their demands aren't met. This chapter talks a bit about demon religions. Yusuke gets the gang back together, this time including Kuwabara. They use Kuwabara's dimensional sword to break in. Despite a ton of time being spent on talking and planning, the group defeats the cultists easily (not presented in a comedic way). The laser is set to go off in a few moments and is set up so that one button will activate it, one will make it blow up, and one will shut it down, with no way of knowing which is which. Yusuke evacuates everyone and stays behind. The button he pushes appears to make it blow up.
175: Final chapter. It's years later and they make it look like they're visiting Yusuke's grave, but he shows up and it turns out they're visiting Genkai's grave. Yusuke smokes now. At this point, it's the final episode of the anime, except Yusuke's there from the start and there's some stuff about the previous chapter.
Having finally read all that, I definitely prefer how the anime ended. They did a good job taking the interesting bits spread out among these chapters and presenting them in a way that makes actual dramatic sense. That "last mission" was really dumb, besides how it actually had Kuwabara do something. By the way, there's nothing that implies Yusuke stopped being a detective after that, which I've heard some people mention before, so it probably isn't really his last mission.