So-called marriage means to maintain the wrong perception for life (結婚とは勘違いを一生涯し続けることだ, kekkon to wa kanchigai o ichi shougai shi tsudukeru koto da) is the twenty-second episode of the Gintama anime.
A mysterious nearsighted Kunoichi suddenly appears alongside Gintoki, yet this turns out to be a ploy to use him for her latest mission.
The Episode introduces us to Sarutobi Ayame, a.k.a. Sachan, a former ninja member of the elite squad Oniwabanshu, who is on a mission to assassinate an Amanto black market merchant called Nezumiya. Due to her clumsiness of dropping her glasses all the time, she can't see very well and by the time she finds her glasses she is ambushed by the Nezumiya's guards and she is forced to leave with her plan having failed. As she tries to escapes, she falls through a roof in a building. The next morning Shinpachi and Kagura go to wake up Gintoki only to find the ninja girl on top of him. They accuse him of picking her up because of one of his usual hangovers and that he was a weird fetish in ninja cosplay. Sachan takes advantage of the situation and demands that Gin takes responsibility for what he did to her and wants to get married. Sachan begins to work around the house with Gin being extremely harsh to her, because she messed with his pudding. This brings Sachan's masochism to the surface. Along the day, Sachan follows Gin around, who continues to humiliate her even in the streets, to her delight. Later at the same day, Sachan receives a call from Nezumiya that he has captured her partners and invites her to his mansion. She has Gin come along to rescue her partners, under the guise of taking him to meet her father for marriage approval. They inflitrate Nezumiya's mansion and they take out most of the guards they come across, while also avoiding every trap. Sachan makes a run to save her partners leaving Gin to deal with the rest of the guards. She dresses as one of Nezumiya's guard and tries to save the hostages, but she messes up yet again because she wasn't wearing her glasses. At that moment, Gin arrives and knocks out Nezumiya. The next day Sachan tends after Gin's wounds apologizing for using him in such a way. Gin walks away without minding at all and tells her the next time she will need help, she should properly come at the Yorozuya and ask for their help.
- One of the guards in Nezumiya's mansion can be seen dressed as Jason Voorhees from the Friday The 13th movies franchise and another as Freddie Krueger from A Nightmare on Elm Street when they chase around Gin.