Miroku meets InuYasha and his friends after walking away from a town after cheating a rich man there out of some money. While bathing in a hot spring, he sees Kagome naked, also taking a bath. He discovers she has shards of the Shikon no Tama (The Jewel of Four Souls) while staring at her and takes them (the jewel shards) and her bike (which he somehow knows how to ride) with the help of his tanuki friend, Hachi. InuYasha and Kagome catch up to him and InuYasha attacks him, but Miroku uses his Kazaana in return. Kagome, realizing that the monk will not harm humans, stands in its path and causes Miroku to quickly cover it with his prayer beads. Miroku explains his situation, and InuYasha reluctantly allows him to join them.
Miroku has habit of asking countless, random women to bear his child, which is formally known as womanizing. He does this because if he would happen to die while in the process of killing Naraku, he would want his son to finish the family mission. Despite his good looks and temperament, Miroku's worst vice (and best running joke) is lechery, specifically shameless flattery and occasional groping with varying subtlety. He is a big flirt that always asks seemingly single women to bear his children. It is known that he had a foster father, grandfather and father, but no trace of a mother. Miroku must have a child in order to have an heir by the time he may be killed by the curse, and thus finds it perfectly fine to offer the chance to many young women to bear his child. This lessens, but does not disappear completely, after he becomes engaged to Sango.
In fact, it was lechery that got Miroku's bloodline into trouble in the first place. His grandfather was fooled into "caring" for a young woman, who turned out to be Naraku in disguise. It was then that he received the Kazaana curse. Despite knowing this, Miroku continues his ways. As an ironic twist of fate, one episode of the anime lands Miroku in a similar situation where he woos a young woman who turns into an insectoid yōkai. His Kazaana suffers a dangerous rip before he destroys the yōkai, forcing him to seek medical attention from his old caretaker, Mushin.
Nonetheless, the monk mellows out as time goes on and proves to be a very valuable ally. He is very knowledgeable about yōkai, and is the secondary fighter of the team after InuYasha. Though quite possibly the most intelligent of the group, Miroku often uses humor or lechery to lighten serious situations, especially if anyone is worried about him. Despite his lighthearted and lecherous exterior, it is clear he has an inner darkness (Shippo has been heard to comment that he "never bought that holy man routine") and worries over his curse and the resulting death sentence that hangs over his head.
There are two main weaknesses of this attack; if he absorbs something with demonic poison (such as Naraku's insects known as the Saimyōshō, or cursed zombies, or anything with a tainted aura such as the water from the god Numawatari) the poison will be spread to Miroku. Because of his holy powers Miroku has a strong resistance to demonic poisons but too much of it can kill him. The other weakness is that if some sharp object such as a knife is sucked into the hole and manages to pierce a side of the hole, then this injury must be repaired otherwise the hole will begin to grow at a much faster rate and thus eventually kill him sooner than his time. Such as in episode 28 when Miroku sucks in the giant mantis. Another good example is when, in InuYasha The Movie: Affections Touching Across Time, Hyoga's underling Ruri uses her spear to expand her own copied version of the Wind Tunnel and is consequently sucked into it, killing herself.
During chapter 448 of the manga, Miroku attempted to use the Kazaana on the merged Naraku and Mōryōmaru, but absorbed the Fuyōheki in their place, thus allowing Naraku/Mōryōmaru's youki to be detected once more. However, he also absorbed a large amount of shouki (miasma); though he was purified by Kikyo, the shouki had cut wounds deep into his body. Now, continued use of the Kazaana will increase these wounds as well, until they reach his heart and kill him.
As of Chapter 536, the Wind Tunnel has reached its limit, opening it one more time will mean Miroku's demise. However, as of Chapter 548, when Naraku has been hit by InuYasha's reformed Meidou Zangetsuha, the Kazaana ceases to make noise, meaning that it has been calmed down, and by Chapter 549, as stated by Miroku, it has begun to close. In Chapter 553, right after Naraku's death, Miroku takes off his glove and sees that the Wind Tunnel has definitely disappeared.
InuYasha may not like how the monk approaches life, but he does respect the monk for his battle skills, knowledge of yōkai, and other worldly skills. They have saved each other's lives several times, and both know that they can implicitly trust each other to help if they are in trouble.
When they first meet, Miroku asks her to bear his child, and promptly gropes her though he does not perform either act again. He enjoys her mother's home cooking (and Kagome's own when she brings it, such as in InuYasha the Movie: Affections Touching Across Time), is respectful of her newfound combat skills, and often sides with her during her arguments with InuYasha.
Like InuYasha, Shippo disapproves of the monk's methods, but also recognizes a good ally. Miroku and Shippo rarely interact directly, but when they do, it is as friends and comrades, or when Miroku "Has to tell him when he's older".
Miroku's partner-in-crime before Miroku met InuYasha and the others. This tanuki jūjin would act as a yōkai and the sneaky monk would pretend to drive him off. The hōshi would then collect from the yōkai's "victims." Hachi is very loyal to Miroku, and their friendship is very solid. In the second movie when Hachi fell from the sky, Miroku worriedly runs over to him. Thinking Hachi was dead, Miroku began to mourn his friends loss only to find him just sleeping. Due to Hachi's friendly nature, he is very polite and congenial to others.
When Miroku and Sango meet, Miroku restrains himself out of sympathy. Miroku and Sango are constantly getting into fights. However, Miroku once proposed to Sango and Sango accepted. After the proposal, Miroku still flirts with other women, albeit less than before. As the story progresses, it becomes clear that Miroku is falling deeply in love with Sango but since he is unable to come forth with those feelings, he hides it behind inappropriate groping and double entendres. Since Miroku is "technically" a Buddhist priest, Sango usually addresses Miroku with the respectful term houshi-sama (houshi means Buddhist priest, and -sama is a respectful honorific), even when he acts disrespectfully, which is reflected in the dub by dryly calling him "monk".
Despite their "cat and mouse" relationship Sango and Miroku actually make an excellent pair in battle, and whenever the group splits up its usually split between InuYasha and Kagome; and Sango and Miroku. Ironically, with all his groping and innuendo, Miroku doesn't ask Sango to bear his child (as he does with every woman he meets). It is not until she demonstrates jealousy over his asking other women and finally brings the subject to his attention. Surprised, Miroku naturally asked the question, and Sango gave him a typical response.
In episode 118 of the anime series, when Miroku and Sango were battling on Mt. Hakurei, Sango was struck unconscious by Hirakotsu. Miroku then cries out, and picks up Sango and Hiraikotsu while running. Kagura then taunts Miroku, saying that he would have lived a little longer if he had run immediately. Miroku then confesses out loud that Sango is the woman he loves, and he would even sacrifice his very life for her. With that, he opens his Kazaana and sucks in all the yōkai and saimyosho (poisonous insects) chasing after the pair.
In Episode 132, Miroku saves Sango from a demonic salamander egg she was forced to swallow, which caused her to repeatedly attack him. Unfortunately, to save her, Miroku was required to defeat Sango in combat, having to punch her hard in the stomach so that the egg could be vomited out. He was injured during this fighting, but nevertheless, he was guilty over his actions. Miroku gets Sango alone with him and asks her forgiveness. She replies that it wasn't his fault since she let her guard down. Mustering his courage, Miroku then lets his heart out to Sango and tells her that she's the only woman he's ever loved. He then promptly proposes marriage to Sango (also asking her to have at least ten to twenty children with him), and she tearfully accepts. However, she follows up her "Yes" with the request that he stop asking other girls to "bear his child". His failure to directly answer her receives a dirty look from her, but nothing else.
It becomes evident that Miroku holds a jealous streak of his own on several occasions, including episode 78 and episode 161. In episode 78, Lord Takeda Kuranosuke has shown interest in Sango for around six years (since he first saw her), and declares he will wait for her for as long as it takes, his love is unrequited. In the closing scene of the episode, Sango shares an umbrella with Miroku (an act that often has romantic implications in Japanese culture). The moment is spoiled as usual by a grope and slap exchange. In ep. 161, Miroku makes it blatantly clear he will not have others pursuing Sango. There is another one of these instances in the manga only, when the group confronts a mysterious medicine man that has a medicine that can "cure all" (manga chapters 358 and 359, "Medicine Vendor" and "Illusion"). The medicine man sees Sango's beauty and decides she can aid him. Though he plans to suck her blood so that he can return to his original form (a mosquito), Miroku is unaware of this. Upon seeing them huddled together on a lilly pad, he rushes in and promptly places many strikes on his head, according to Shippo. He exhibits a similar reaction in chapter 485 of the manga, when Yakuro Dokusen gropes Sango, supposedly to check the strength of her loins, which prompts both Miroku and Sango to kick the sage in the head and Miroku to threaten Yakuro Dokusen against any other inappropriate actions.
In the third movie, InuYasha The Movie 3: Swords of An Honourable Ruler, he also says the following line to Sango: "Besides, what's the point of living with this cursed hand...when I can't even use it to protect the woman I love?"
As of the fourth film, InuYasha The Movie 4: Fire on the Mystic Island, Miroku and Sango are still engaged to be married after Naraku's defeat.
In chapter 523 of the manga, Sango finally kisses Miroku, however it is unknown if he was aware of it since he was unconscious.
In the manga, at the end of the series, we are told that it is three years later, and we are shown that Sango and Miroku are married and have three children, twin girls and a boy.