Graduate student Souichi Tatsumi is demanding, violent, tyrannical... and a homophobe. So, it's unfortunate that his best assets are a beacon to the homosexual eye: his ass and crotch. Unfortunate, indeed--for both him and his underclassman/lab assistant, Tetsuhiro Morinaga, who is hopelessly in love with those assets despite the threat to his own personal safety
The story picks up on Morinaga and Souichi's story where Challengers left off. Tetsuhiro Morinaga is a university student with a 4 year crush on his senpai, Souichi Tatsumi, who he assists with his research projects. In Challengers, while sick with a cold Morinaga inadvertently confessed that he was gay and in love with Souichi. He thought that Souichi would hate him since he is homophobic and so he said that he was going to leave school but Souichi insisted that they just forget about it and stay friends. Their story ends leaving Morinaga convinced that his feelings will never be reciprocated.
At the start of The Tyrant Falls in Love, in 2004, Tomoe and Kurokawa had just moved to California for Tomoe's new job and Souichi hears that California has just legalized gay marriage. Souichi furiously calls Tomoe to tell him he should not get any ideas about getting married but Tomoe had not heard about it at all since he had been busy working so Souichi's call did the exact opposite of what he wanted it to do and Kurokawa and Tomoe run off to get married. Souichi runs around yelling that he's going to go to America and kill Kurokawa and get a green card so he can become the Governor of California to re-ban gay marriage. Morinaga convinces him to calm down and drink with him instead and so he goes Morinaga's apartment to drown his sorrows. After Souichi drinks all of the alcohol they had bought he demands that Morinaga goes out to buy more and while Morinaga is out Souichi searches Morinaga's apartment for alcohol and finds and unwittingly drinks an aphrodisiac Morinaga has been given by his friend and hidden. At first it seems that it had no effect and Morinaga thinks he has been tricked by his friend. They go to sleep but Souichi wakes in the middle of the night to find himself aroused and so he tries to sneak off to relieve himself but he accidentally wakes up Morinaga because the aphrodisiac has made him weak. Morinaga offers to help him relieve himself and even though Souichi refuses he still does. After he has released once Souichi is still aroused and Morinaga, unable to restrain himself any longer, has sex with Souichi even though he tells him to stop.
The next morning, after Souichi throws Morinaga out of his own apartment, Morinaga goes to the university. When he returns home Morinaga calls Souichi and apologizes and swears to never appear before him again. At first Souichi thinks nothing of it because he is angry at Morinaga but after he is completely missing for two weeks, Morinaga's classmates come and ask Souichi if he knows where Morinaga has gone. Souichi is shocked. He just thought that Morinaga was avoiding him and is really worried and goes searching for Morinaga but he is no where to be found. Morinaga eventually returns to his apartment to pack up his stuff so he can move away when Souichi finds him. Souichi lets slip exactly how worried he was about Morinaga's disappearance. Morinaga is touched that Souichi was so worried. Souichi tells him to never go away again and Morinaga tells him that if he is to stay they will have to have sex and Souichi reluctantly agrees. The two commence a dysfunctional relationship which develops slowly into a romance over the course of the series.
Souichi Tatsumi - a first year doctorate student in the agricultural science department at a university in Nagoya. He hates gays because he was almost raped by a gay professor. He is voiced by Hikaru Midorikawa.Testsuhiro Morinaga - a first year masters student in the agricultural science department at a university in Nagoya. He has been in love with Souichi since he first set eyes on him. He is voiced by Kousuke Toriumi
Hiroto - Morinaga's friend. He works as a bartender in a gay bar called Adamsite. He often gives Morinaga advice on his love problems. He is voiced by Daisuke HirikawaKanako Tatsumi - Souichi's 14 year old sister. She mistakenly believes that Souichi and Morinaga are a couple, a belief that becomes less mistaken over time. She is voiced by Ayaka Kyo
Taichirou Isogai - Mitsugu's friend and ex-coworker. He accidentally finds out about Souichi and Tetsuhiro's relationship and uses it to blackmail Souichi to stop threatening to kill Mitsugu. Voiced by Toshihiko SekiTomoe Tatsumi - Souichi's younger brother and the main character of the manga Challengers, He is very smart but ditzy and absent-minded. He is voiced by Kouki Miyata.
Mitsugu Kurokawa - Tomoe's husband. He was one of the main characters in the manga series Challengers. He lives in constant fear of Souichi and is deathly afraid of him. He is voiced by Tomokazu Sugita
Kunihiro Morinaga- Tetsuhiro's older brother. Voiced by Ken Narita.
Junya Masaki - Tetsuhiro's first love and Kunihiro's best friend.
Soujin Tatsumi - Souichi, Tomoe, and Kanako's father.
Yamaguchi - A friend of Morinaga. In the same year and major as Morinaga.