Who is Miroku?
Miroku is a young monk (Houshi) that is seeking Naraku to break a curse that has been placed on this family, and thus passed down to Miroku. The curse is of a windtunnel that is in the palm of his right hand. When released, the wintunnel sucks up everything in its path. Unfortunately, the tunnel is unruly, and will soon grow out of control and suck Miroku up inside it as well. That is his fate, as has been the fate of his family before him. But Miroku doesn't let that get him down. Nope. He's a complete leacher. Every girl he meets he asks to bear his child. Miroku's left hand seems to have a curse on it, as well. This curse causes him to pet the bottom's of pretty ladies, which gets him slapped quite often.
Quote: "Will you bear my child?"

Who is Sango?
Sango is a demon slayer, the only surviving member of her village. The rest of them were slaughtered on a demon hunt when Naraku possessed her little brother Kohaku and had him kill everyone. Sango is tracking Naraku to punish him for what he did to her brother, and for what he did to her village. She never gives up hope that she can save her brother from Naraku's spell, and they can be together. Sango's weapon is called the hiraikotsu (imagine a BIG boomarang). She has a companion in the demon cat Kirara, who is cute and cuddely one second, but fierce and firey (ha ha, pun intended) the next.
Quote: "Is it necessary to keep stroking my leg while you talk?"

What's this about a relationship between Miroku and Sango?
Sango and Miroku travel alongside the present (well, their future) Miko, Kagome; the half inu demon, Inu Yasha; and fox demon, Shippou. Together, they all seek Naraku for their own revenge, gathering jewel shards along the way, and fighting various demons that come to test out the strength of their own jewel shards, or to try to take Kagome's. Traveling from village to village, the group meets a lot of different people that they have to both fight or save. Miroku, in typical fashion, hits on every woman he sees. After a while, us as watchers/readers sees the tension that builds in Sango each time Miroku lays his hand on another woman or asks her to have his children. Sango denies this adamantly at first.

When a young face from the past shows up, a woman that has agreed to have Miroku's baby, Sango's true feelings begins to surface, as when Miroku gets lured in by the demon possessed Princess that Sango catches him kissing and has to save him from! It ends with them sitting together... so cute. Miroku takes her hand, but promptly begins to caress her in a place that gets him smacked. Oh well. Miroku confesses at one point when Sango leaves that with her gone, he can finally relax. Why is he tense?! Huh?! Huh!? Shippou asks the same question. Miroku doesn't admit to anything, but it's obvious that Sango puts him on edge because he makes an effort to be conscious and aware of her. He's tested later on when a lord Sango saved from demons years before proposes to her. Poor Miroku pretends to be his same calm, logical self, but it's obvious the idea of her marrying someone upsets him gravely.

And we can't forget in movie 1 how much time Sango and Miroku spent alone, fighting demons and saving one another. Remember the scene when Kagome dropped into Inu Yasha's arms from the back of the flying Kirara? Also, remember that Miroku looked thoughtful before opening his arms to bid Sango to do the same? It would have been a sweet moment, wouldn't it, had she not dropped her mask on his head instead.