i think it was called "brothers" or something. Here's what I remember: Naraku's new minion appears & uses a green emerald stone on the swords. The 2 swords get connected, forcing Inuyasha & sesshomaru to stay within a range of each other. So sesshomaru has no choice but to join the inutachi.

I think before this happened, they all get stuck in a cave together because of the rain. They (except sesshomaru & jaken) play "truth or dare". Miroku tells Rin to ask inuyasha where babies come from. Shippo dares inuyasha to tell sess that he loves him. Etc...

I think in ch9 or something, it starts with "sesshomaru is bored." The girls & rin are taking a bath. Sessh is bored so he tells jaken "rin forgot her soap" & tells him to take it to her. Jaken eagerly obeys & gets beaten up by the girls. Etc.
Then Kouga shows up & rin starts to scream & then kouga runs away. Etc.

Does anyone know the title or author of this story?

No I don't sorry, but I want it too now!

I found it:) It's called "brothers" by AceOFDiamonds....but it's still not complete:(