Yoshiwara is besieged by an incense where whoever smells it, falls for the first person they see. First it was Tsukuyo and in trying to destroy it, things go downhill when it affects everyone.
Two girls walk down a bustling street in Yoshiwara. The black-haired girl tells her blonde friend that the district was a place where women were forced to like unlikable men but she wasn't sure if she was able to do so. She tells the blonde that for women who can't do so, there exist a secret Yoshiwaran drug that can make people fall in love automatically. She wonders if they can fall in love over and over with anyone but the blonde is unsure since she had never had an infatuation before. The black haired girl admits that she had a crush on a boy in her village but was never able to confess before leaving and wished that she had the drug to enable her to confess. The blonde asks her friend, Hotaru why she wishes to rely on something like that to express her feelings. Hotaro agrees but understands how difficult it is to express oneself to someone you love or hate. She hopes the blonde, Tsukuyo, will someday understand, too, what it's like to have feelings for someone she loves.
In the present, Tsukuyo and her Hyakka stop a couple trying to run away. She chastises the woman, Hotaru for trying to elope with someone who wasn't the man of her village and the man for trying to steal Hotaru and the money other courtesans earned. The desperate man attacks Tsukuyo, resulting in him being pinned to the wall with kunai. A Hyakka ninja tells her boss that Hotaru was inflicted with something and the blonde confronts the man on what he did to her. Something heart-shaped falls out of his yukata and Hotaru tells them that the man forced her to smell something that caused her to go crazy. Unfortunately, ash from Tsukuyo's pipe falls on the heart, producing a smoke that she accidentally inhales. The Hyakka panic and try to find a way to put it out; instead a wandering drunk figure on the roof pees on it. They reveal the heart piece was an incense that affect the brain where the first person the infected sees after smelling it, will fall in love with that person. The first thing Tsukuyo sees after smelling the smoke was the drunk man's genitals; worse, the drunk man is ... Gintoki. He wonders why the girls below was playing with fire until he recognizes them and Tsukuyo throws a kunai at him, launching him out the district. The enforcers are happy that Tsukuyo wasn't affected by the smoke but despite Tsukuyo agreeing with them, her love-struck expression says otherwise.
The next day, Hinowa takes care of Hotaru and gives the Yorozuya more information on the heart-shaped incense called Aizen Kou. The dangerous incense have been causing some commotion in Yoshiwara: courtesans have been caught stealing money and eloping, while some customers have been attacking each other over courtesans. Both Gintoki and Hinowa agree that using the incense to create fake love is nothing compared to real love. Tsukuyo returns and informs the others that she caught a few men wielding the Aizen Kou but they were in no state to give her information due to overdosing. She wonders how long the effects last but Hinowa responds that it depends on the dosage...and asks why Tsukuyo was sitting far away from them. Tsukuyo, still affected by the incense, decides to stay far away from Gintoki as possible to still retain her sanity. But she is asked to come closer so they can think of a strategy and she ends up sitting very close to Gintoki. She tries to dissuade everyone's concerns over her by creating a plan to find and confiscate the Aizen Kou but her affliction bleeds through in trying to find ways of being with Gintoki. Tsukuyo decides the best course of action is to give the gathered incense in a cart to the Yorozuya for disposal so she will be able to act normally when Gintoki leaves. But in her altered state, realizing that Gintoki is leaving causes her to jump into said cart. An annoyed Gintoki tries to pull her out by her hand but surprised by the gesture, she pushes him away. This leads to him accidentally landing on the handle, flinging the large pile of incense into an open flame of a vendor's cart.
Meanwhile, Tae and Kyuubei visit Yoshiwara for shamisen lessons, with Kondou secretly watching from the rooftop. Tae tells the worried Kyuubei that it was fine to visit the district as Tsukuyo was protecting it and decides to visit the ninja courtesan. She notices the incense smoke and wonders what is happening. Back to the others, the smoke spreads and Tsukuyo guides the people away from the smoke, asking Shinpachi and Kagura to find water to put out the fire. Wondering where was Gintoki, the teens enter the first house they see to ask for help... just to see Gintoki and an old woman naked in bed (Although the two didn't do anything as Gintoki was unable to perform). They tearfully return to Tsukuyo, who was able to put out the fire, to tell her that the sliver-haired man was affected by the smoke and is now flirting with the elderly women. Tsukuyo and Kagura try to talk some sense into him, Kagura even reminds him that he was subconsciously repulsed by the old women. Gintoki instead sexually flirts with the girls and Tsukuyo and Shinpachi horrifically realizes that thanks to inhaling a large amount of the smoke, Gintoki has become a lecher for all women. The blonde woman tells the teens to flee but the duo are hit by a blast of Aizen Kou smoke that someone has unleashed around the entire district. Shinpachi and Kagura were able to close their eyes despite smelling the smoke but accidentally bumped into each other, opening their eyes. They both ended up falling in love with... Shinpachi's glasses (Shinpachi seeing his reflection in Kagura's eyes); embarrassed, the teens flee.
Tsukuyo finds herself surrounded by afflicted men wanting to spend time with her and they attack. Gintoki saves her, declaring that she and all women belong to him while beating them up. The two flee and hid in an alley filled with afflicted courtesans whom he "saved". To make sure that the courtesans are safe, Tsukuyo suggests that they should be taken to Hinowa while she finds the perpetrator behind spreading the Aizen Kou all over Yoshiwara. Gintoki refuses to have her going alone, so he should go with her and believing that her anger at his afflicted behavior is jealousy suggests that she wants Gintoki to only be his. The still afflicted woman falls for his smooth talk and asks to hold his hand. He happily agrees and brings in the affected Kyuubei and Tae so they can all hold hands. Tsukuyo berates him for putting the two girls under the incense's effects but he responds that he hadn't "touched" them yet. Until the duo suplexed him. The blonde is surprised that the two hadn't fallen for him due to the incense but Kyuubei and Tae fail to convince her that they weren't affected. The duo put Gintoki in a chastity belt with a ball and chain connected to his crotch to make sure he won't go off and attack other women. They and Tsukuyo fall into an argument on what to do with him and Gintoki tries to use this chance to escape, just to encounter an afflicted Kondou and all the other males only wearing the same chastity belts. Tsukuyo is then tied by Kyuubei and Tae while Kondou proclaims their submission to someone named Aizen Myouou. Gintoki and Tsukuyo find themselves surrounded.
Shinpachi catches up to Kagura but the Yato desperately struggles not to look at Shinpachi's glasses while Shinpachi tries to get her to look at him to see his reflection in her eyes. The two proclaim that they will only have eyes for each other then abruptly poke each other in the eyes, returning the two to normal. They are interrupted in their squabbling by a voice that declares that love is an illusion which can fade and even die. Eternal love doesn't exist, a sad story is love's brevity. But she will bring everyone to love only her and she will love them all in turn forever. The teens see a procession of afflicted people, including Kondou, Kyuubei, Tae, Tsukuyo and Gintoki. In the front, being carried on an elaborate litter, was the perpetrator... Hotaru!!
- Hotaru (debut)
- Sakata Gintoki
- Shimura Shinpachi
- Yagyuu Kyuubei
- Shimura Tae
- Kondou Isao
- Koto is a long Japanese stringed instrument usually having 13 strings (there exist Koto that has at least 17). It is the natural instrument of Japan.
- Shamisen is another famous Japanese stringed instrument that has three strings. It comes in a verity of shapes and sizes depending on what it will be used for.
- When Tsukuyo throws Gintoki while he was moving the incense, he cries "Kshatriya", a Mobile Suit whose pilot is Marida Cruz, a character from Mobile Suit Gundam UC who is also voiced by Kaida Yuuko.
- Aizen Myouou is the name of a Buddhist deity of love. The incense's name is a pun on it.