The universe keeps trouncing on Madao because of karma relating to something he did in his previous life.He was Gendo and Akainu
The story will end with everyone being arrested.In the very first episode, Shinpachi says he was arrested for the murder of the ambassador (which Gin committed). There's no mention of acquittal, so it's likely that he's still wanted. In addition, he got into a gang fight at least once, as well as going into a Love Hotel when he was still underage. Gin probably has a thousand counts of murder, assault, kidnapping, and fraud under his belt by now, and he illegally used a metal sword during the Benizakura arc. Kagura is an illegal immigrant, was in with Yakuza, and is also guilty of theft. They've only evaded pursuit all this time by their friendship with the Shinsengumi and entertaining the Shogun on occasion. The final episode will end with all of them being arrested by the cop whose auto Gin totaled in the first episode, who has been pursuing them all this time. At 400+ chapters, it will be the longest Brick Joke in history.
The story ends with the Fourth Wall so broken, the Gintama cast ends up in our world.If you think about it, it makes a lot of sense. Already, Gintoki and co. broke the fourth wall so many times, that there will be nothing left of it by the end.
Elizabeth eats people.All one-time characters, such as Catherine's gang, the hosts, and Appo's family, are actually eaten by Elizabeth promptly after their story finishes. (He only pretended to like that nurse so he could lure her into the woods to eat her.) He knows he can get away with this because everyone in Katsura's group ignores him and Gin's memory is too bad for him to remember all these people.
Assault of the shogun's castle arcFor some reason, probably the kiheitai, the shogun and his family will be in danger and Gintoki, Shinpachi, Kagura, Sadaharu and some of their friends will go to the rescue, and Kagura will re-encounter with her friend. Gintoki and Hijikata will fight together against a common enemy.
Benizakura was, in fact, a prototypeBenizakura was powerful but not perfect, I think that it was a prototype and Takasugi's plan is a more powerful weapon, maybe not a katana, but become the entire body in a powerful weapon.
The Shiroyasha OVA is canonAnd the one who slashed Takasugi's eye is one of the Tendoshu, as seen by his hat and cloak.
Mutsu is a yato memberIt was never mentioned if she is human or amanto, and her clothes fits with the yato tribe's habit to cover from sun.
In the manga, Elizabeth is a yato memberNot the renho Elizabeth, the one from Benizakura. Come on, Gintoki, Sakamoto and Takasugi each have yato allies.
Yoshida Shouyou, was the most powerful Samurai in Japan before his death.Think about it for a moment. Only skilled Master Samurai are able to teach students like Gintoki, Katsura, and Takasugi, boys totally different from one another and guided all of them under a common Bushido Code. We know nothing about his past other than the fact that he taught these kids to be the most powerful Samurai in the Edo. If he taught them the way of the Sword, then imagine what he would be like in his Prime! Even now, many years after his death, his beloved pupils still have high respect for him. Katsura told Takasugi during the Benizakura Arc that Gintoki took Shouyou-Sensei's death the hardest. His death changed everything about what they believed in and altered their Bushido Code to fit their own personal beliefs.
Yoshida Shouyou was part of the Naraku.Both Oboro and Nobume knew him very well. Oboro refered to him by his first name, without honorific, so they were most likely friends. Oboro also mentioned there being "3 feathers" of the Naraku. One of them was Nobume, the Oboro was likely one too, and Yoshida Shouyou could have been the third.
Gintoki will use Tatsugoro's jutte in every "serious arc"Jossed, considering the fact that there's been "serious arcs" without the jutte.
Gintoki is actually a time lordThe anime isn't actually running on Sazae-san time, it's just that Gintoki caused some sort of weird timey wimey effect on the people around him. And possibly the whole of Japan.
Yoshida Shouyou and Madao ex-wife are related/the same person/reincarnationMy point? They're the only two characters with no face shown above the nose.
The Terminal will be the site of the final battleMainly because it's the largest structure in Edo and it'd make a kickass location for Gintoki and Takasugi to duke it out, just as shown in the episode featuring the fake ending scenes. In addition, part of Takasugi's plan will be to use all the energy accumulated in the Terminal and blow Edo sky high.
The Gintama Movie will end with Gintoki meeting his future self, who will reveal that the plot of the entire movie was just a prank pulled by the future castSince when has Gintama ever taken itself this seriously?
There will be self insert arcGintama had makes fun of a lot of fanfic tropes : Age-change arc, Genderbender arc, and now bodyswap arc. There will be a self insert arc, complete with Mary Sue OC who will fall in love with a Draco in Leather Pants character. Maybe Takasugi. Also, there will be shipping wars included.
The baby in the infant strife is actually GintokiThe movie revealed the time machine indeed exist. The baby looked like Gintoki himself. For some reason the baby (or the toddler, having grown up) would ended up travelling to the past, where he would grow as an orphan named Gintoki and adopted by Shoyo.
The speculation of the last chapterGintoki would hit someone again with this scooter and this time, he is using the time machine to reverse the damage.
Gintoki and Oboro are relatedI'd bet on brothers, as they look around the same age. Basing this mostly on their similar looks and combat ability: they both have white hair, (though Oboro's seems more wavy compared to Gintoki's curly), and they seem to have similar tactics, like using pieces of their broken weapons to attack the enemy. Both of them have also recovered from wounds that really should have killed them, too...
During his life, Yoshida Shouyou was a troll
WMG about Saitou from Shinsengumi
Kamui will die...but not because of a fight, he died protecting Kagura instead.