It would have to start out with an Osuwari.
It would have to contain Kagome freaking out about Inu going to hell.
It would have to have appearances of Kikyou as Bitch Goddess who comes by to say, "Inu, we're going to hell NOW," while calling Kagome rude things, and Kouga must appear as stupid, won't-take-no suitor. He must fight with InuYasha, and InuYasha must get sat.
Shippou would of course have to get Inu sat at least once.
Miroku must say suggestive things to something Inu says, and make Inu and Kagome blush at least once. He must anger Sango at least once and get slapped and/or hit in the head at least twice before the story is over.
They have to fight a bear or snake youkai.
Kagome must storm off to the well at least once.
There must be a hot springs scene.
Inu has to peak at Kagome sleeping in her bed in the future at least once.
Inu and Kagome must share a first kiss by either the hot springs, the well or the Goshinboku. If there is a lemon it MUST be out of doors at one of these locations.
If there is a lemon, Inu, the shy man who was never allowed much contact with people growing up, must turn immediately into the most skilled of women pleasing lovers after cutting her clothes off with his claws. He must mark her by biting her on the shoulder near the neck.
Optional Items: Inu may turn youkai after Kagome gets injured by powerful youkai. If so, he runs off with her, treats her wounds, and they have first sex, doggie style. Youkai InuYasha cannot be fully intelligent, and loses most ability to speak.
Kouga may be allowed to come around one more time after mating so that Inu can beat him into a bloody pulp.
Kagome may be allowed to pulverize Kikyou after mating.
Now, have I forgotten anything?