After an hour of extensive googling, I think I might have stumbled upon an answer.
Gintoki screaming Psycho Pass! when hit by the chair,
is a reference to a scene from the Psycho-Pass series, where Kasei gets hit on the face with a book, thrown by Makishima.
Gintama is well known for using gags and references regarding other animes. Most references are ...
As mentioned on the Wikipedia article on Science Fiction:
Science fiction is a genre of speculative fiction dealing with imaginative concepts such as futuristic settings, futuristic science and technology, space travel, time travel, faster than light travel, parallel universes and extraterrestrial life.
Hence, Gintama is a Sci-Fi anime based on its:
The dog is a smaller version of Sadaharu from Gintama
The colour of the dog is of course Pikachu.
The sword is the Shikai form of Zangetsu, Ichigo's sword from Bleach.
It seems that Gintoki is about 25 to 26 years old.
In the Ask Sorachi segment of Episode 9: “You should go all out in a fight” Gin were described as a "hairless baby" when the Amanto first arrived. Shortly after which the Joui war started.
[After credits and preview]
Class: Teach us, Ginpachi sensei!
Gintoki: Um, this is a question from a Mr. ...
Much like @Akaik mentioned in his answer, the main reason for the inconsistencies is entirely down to both Sunrise and Gori-Sensei not entirely knowing the details of these events as they go head first into making everything.
They pretty much admit to this using Gintoki to explain at the end of episode 306, where they include another Ginpachi-Sensei segment....
Gintama's setting is mix of fictional inter-galactic universe (which might be depicting foreigner coming to Japan during that era) referencing to actual Japan historical era specifically Bakumatsu period.
In 1876, samurai were banned from carrying swords. A standing army was
created, as was a police force. This "sword hunt" was performed for,
The Sword Ban was enacted because they feared of the Samurai's ferociousness. During the Amanto War, although the Samurai's main weapon is sword, they managed to deal massive damage, especially the group lead by Sakata "Shiroyasha" Gintoki, Katsura "Runaway" Kotarou, Takasugi Shinsuke, Sakamoto "The Dragon of Katsurahama" Tatsuma. The main reason behind the ...
This running gag in the Gintama anime is actually from Doraemon. They are referencing to how the entrance to a time machine is available at a hole similar to a drawer, which is exactly where the time machine is in the Doraemon anime. Here is list of the other parodies present in Gintama. LIST
The drawer entrance to the time machine.
Here is one possible viewing order taken from Gintama Reddit FAQ
What is the watch order of the series?
Skip episodes 1 and 2. They were a special to celebrate the series getting animated.
Gintama: 3-201 (The arc at eps 58-61 was made into a movie. Watch it if you don't care about spoilers, instead of the the arc in the series.)
Gintama Movie 1: Benizakura (...
There are hardly any lists around that list them by episode, but if you want the lists, there is one on the wikia, though it is complete, it just lists them.
However, a better one, albeit being a little incomplete is available on tvtropes. This list is incomplete but it lists them in order according to the references.
Well, there's nothing stopping you from watching the newer episodes :)
Gintama is mainly episodic (as in, not much ongoing connection from episode to episode) so it's probably okay to do so. You might miss out a few references to past episodes though.
Of course, if you want to enjoy it fully I'd recommend you start from the very beginning.
The Anime Gintama has a lot of side stories. Kintoki Skata is one of those characters in those side stories. The reason why the main focus was on him was because he looks like Gintoki and he also carries the same name except that his name starts with K not G. There is no more information about him yet in the manga. However, there is a possibility that he ...
It's mentioned here:
Apparently, the author miscalculated in trying to estimate on when the series will end. He mentioned that in Jump, mangaka have to notify the editorial department 6 months in advance before the date that the manga is expected to end.
However, he seemed to have realized after informing the editorial department that he could not fit ...
For the record, here are the rest of the references:
The color of the dog references Pikachu from Pokemon.
The guy's hair references Death the Kid from Soul Eater
The guy's face references Goku from Dragon Ball
The whiskers belong to Naruto Uzumaki from Naruto
The hat belongs to Luffy from One Piece
The scarf belongs to Natsu from Fairy Tail
I think he's around 23-24. On episode 292, when gintoki wore a 3rd year uniform he said that he's a 9th year, this implies that he's about 23-24 since a 3rd year is usually 17-18.
And on Ginpachi sensei, it was said that 20 years ago, gintoki was this hairless baby, who doesn't look to be more than 4 years old, also when he went to join at the very end of ...
Like mentioned by @Gorp, this inconsistency is mentioned in the Ginpachi-Sensei section of episode 306 and answered by Gintoki. Here's the chronology of what happened, starting from the foundation of the school.
Shouyou found Gintoki in a battlefield.
Shouyou created a school with Gintoki.
Katsura and Takasugi joined the school.
Shouyou and Gintoki entered ...
I'm pretty sure this is because the anime studio Sunrise didn't know much about their past either (the anime studio and the author most of the time don't have much interaction). The scene you mentioned was not shown in the manga but only in the anime.
So you can say Sunrise made a mistake just like how they skipped an important scene from the earlier ...
Yorozuya means Jack of All Trades. Other subs translated Yorozuya into Odd Jobs.
They are called so because they would do any job at all for money. Any jobs ranging from chasing after run away cats to saving the world.
I think the real reason is that Sorachi-sensei actually forget about it. Hell, he even forget about Shinpachi and Otae's goal of restoring their family dojo.
But, here is the interesting thing. After loads of episodes where Shinpachi and Otae's goal was forgotten, a new character named Hajime who was supposed to be Otae and Shinpachi's senpai at the dojo ...
The dance is called Wotagei or Otagei. It is a dance done by Idol Otaku (called Wota) to show support for their idol during the concert. Quoting Wikipedia,
Wotagei is particularly associated with fans of Hello! Project and AKB48 idols, as well as fans of anime voice actresses, who often perform theme songs for the series in which they appear.
Thus, it ...
Whenever dealing with futuristic stuffs, technologies, extraterrestrial lifes, it is categorized as "sci-fi". If you ever watched Gintama before, you should aware that almost every episode has a short prologue. You can see tons of futuristic stuffs going on, like spaceships and aliens.
Still not convincing enough?
How about Space Scene?
Some Weird Looking ...
Don't know that much so I'll just contribute a bit.
Gintama really doesn't stay that true; it's more like taking bits from each real life character's known traits and either using that as inspiration or warping them into something vastly different. As far as Shinsengumi hierarchy, it is loyal- Hijikata was also known as the Demon Vice Commander, Kondo was ...
It could also be the "Kaien" robot from Gintama, here is a picture of it firing from episode 235, and the dirty humor definitely fits the series, although I didn't hear that exact quote in the episode.
and here is the same scene from the manga
Hitotsubashi faction is a faction within the shogunate that supports Tokugawa Nobunobu instead of the current (current as of that part of the story) shogun, Tokugawa Shigeshige. Think of them as the opposition party.
The very fact that Sougo said it means that the government knows about it. However, while they are dangerous, the shogunate can't just kill ...
I don't know for certain, but my best guess is that it's a reference to a Japanese actress called Maki Carrousel, who got a gender reassignment operation in Morocco in 1972. Back then, gender re-assignment surgery wasn't legal in Japan, so people wishing to have it performed had to travel abroad, and the most common location for it as first was Morocco. ...
My apologies, after being sought out I believe I didn't answer or read your question to the fullest.
You asked if any of the managa for Gintama was based on the anime. As I had to re-read your question, the answer to your question is none of it as far as I have read. You said the anime has been done for 15 years is false, the anime(assume your taking about ...