Yashahime four reveals Rin is inside the tree of ages.
Why is unknown. Maybe related to Sesshomaru denouncing his title as a demon lord, consequence was Rin being targeted and trapped. He's trying to free her from that and it has something to do with his daughters helping out. Probably related to the reason he dropped both off near Kaede.
That Sesshomaru would make such a choice shows har far he's developed since the start....motivations changed completely after developing some human compassion, understanding why his father made the decisions he did.
Tree of ages asks the kids to beat one of the dog demon lords, someone who was a rival to Sesshomaru's father, because he has rejected that title similar to Sesshomaru and walked a different path. So something about denying destiny is causing some sort of conflict in this world. Seems to be the key to figuring out what has happened to everyone. I don't think the tree of ages is an antagonist in any way. Doubt Kikyo's visage would be used for that purpose.
The battle vs the root demon was great. Those kids aren't weak at all, and they've yet to even show their demon sides. Next week preview shows Moroha doing just that and adopting Inuyasha's yellow eyes
She's the best part of this sequel so far. Not only because she's a cross between the most liked characters of the original, but has the type of gung-ho personality that's easy to root for. Has been the source of most of the comedy thus far and also spearheads any of the action scenes, of which are pretty well animated.
there's also an image of Miroku in the teaser. Which would have to also mean Sango shows up and so do their kids. But it could be also be a flashback. Miyoga shows up in the preview as well. You'd like to think he knows where Inuyasha is