Roketsu said:
Kano: the freeplanetling.
When she touched the feather (Kanna's feathers possess [sad] memories) as a child, perhaps the sad memory was passed to her. Like the infant in the flashback, Kano had lost her mother as a child. So maybe she was sensitive to that memory -- the separation of a mother and daughter by death. Recall that Yukito felt nostalgic and sad when he encountered the feather that Kano had touched. The magic feather, Yukito's power and Kano's wish made it possible for her to meet and thank her mother as Yukito had suggested she do. This helped resolve her sorrow and guilt over the loss of her mother and I suppose the feather was returned to Kanna with the happy memory Kano experienced by meeting her mother.
Recall also that the bruise on Kano's wrist disappeared with the feather. The child had the bruise, yet Kano was reciting the words of the mother. So she had a connection to both mother and child from the memory.
As to Minagi, well, she's Minagi, not a reincarnation of someone else.
Minagi and Micheru (the buttshaking-ling).
I think Minagi was a bit of a plot device to get Yukito (and us) to realize that the "girl in the sky" was more than just a folk tale or legend. Michiru, Minagi's sister who died before birth, meets the Kanna, the girl in the sky and borrows one of her feathers which enables her to come to Earth as a "dream," in order to comfort Minagi and reconcile Minagi with her mother, emotionally broken by the loss of Michiru.
Michiru's companionship helps Minagi through the difficult time with her mother; Yukito steers Minagi back home where Minagi and her mother are reunited as a family. In the end the mother finally sees Minagi as herself rather than her dead child. Before she leaves (the dream comes to an end), Michiru gets to finally meet her own mother; another happy memory to bring to Kanna when she returns the feather.
So really neither Kano nor Minagi or Michiru played a role in the past (Summer Arc). Neither did Yukito, Misuzu or Haruko for that matter.
Misuzu dreams of Kanna, she is not Kanna herself. She is one of Kanna's dreams, she is part of Kanna, but not all of Kanna. A winged being's essence cannot fully fit into a human being. Like the water of the ocean, it cannot fit into a teacup without shattering it.
Likewise, Yukito is not Ryuuyu, but he does carry on his will. He is descended from Ryuuyu and Uraha, separated by 1000 years. He inherits Ryuuyu's will (to find and save Kanna) and Uraha's power (magic and the doll with generations of unfufilled wishes which will ultimately be used to help Misuzu save Kanna).
Why did I mention Haruko, Misuzu's substitute mother? There's a similar theme between the Summer and Air arcs. Kanna wished to be reunited with her mother, Misuzu has a similar wish: to experience happy memories with her mother. The goal which has taken 1000 summers to finally reach.
When Yukito has an attack in the hallway and is wounded, later to discover a scar just like Ryuuyu's suggests Yukito suggested to me that Yukito has passed the point of no return. He's experiencing the curse that his mother warned him about: caring about the girl will cause both he and the girl to die. Misuzu's dreams are having a physical effect on both Yukito and Misuzu.
The common theme:
Memories and the mother-child relationship. Families stick together.
Each of the girls in the series, Kano, Minagi, Kanna and Misuzu were separated from their mothers either by death or by circumstance. The goal and wish for each of them is to reconcile that loss. Sad memories hold us back, happy memories give us hope and keep us going. But we cannot live on memories alone.
Each of these girls, even Michiru to some extent, resolve that mother-daughter separation and the guilt or sadness associated with it.
Kano meets and thanks her mother. Kano had felt guilty about her mother's death and accepted part of the blame as the reason for her mother's death. Until Yukito set her straight, Kano had wished to apologize (for having been born) rather than thank her mother. Good advice, Yukito!
Minagi is able to reach her mother and be recognized as herself rather than her dead sister. She had accepted her mother's condition the result of her sin: wishing for a younger sister who unfortunately died before birth. She then lived as a fragment of her mother's dream, taking on the role of Michiru, whose death devastated her mother. That dream had to end to bring Minagi and her mother together.
Misuzu lost her mother as a child and was taken in by her aunt Haruko. The two remained somewhat distant in part because Haruko feared losing Misuzu to her natural father, and Misuzu kept her distance because affection resulted in fits and pain. They overcame these obstacles and became close in the end. Haruko ultimately would have lost Misuzu no matter what she did anyway - the least they could do was to create some happy memories.
Yukito guided each of the girls to their respective goals, but ultimately each had to resolve the obstacles on their own to find happiness. Such is life.
All of these happy memories were returned to Kanna who was all alone in the sky.
Finally a word about Sora the crow.
As tragic as it is that Yukito seems to have run away and abandoned Misuzu when she really needed him and cared for him, he did the right thing. He'd gone as far as the two could go with the way things were. Had Yukito stayed as the freeloader at the Kamio house, Misuzu would have died without reaching her goal. Yukito may have lived on, or he may have died within a year anyway, like his ancestor Ryuuyu had 1000 years earlier. This would have solved nothing.
Instead, like his mother before him, he placed his heart, his wish, into the doll while he still had power, while he was still strong. His wish was to be by Misuzu's side forever and to help her reach her goal, and to save the girl in the sky, Kanna, fufilling Ryuuyu's 1000 year old wish. In the final three episodes Yukito, as Sora
rarely leaves Misuzu's side. He intervenes when Haruko tosses away Misuzu's birthday gift, the baby dinosaur, and alerts Haruko to its presence at the temple towards the end. Misuzu tries her best to reach the dinosaur and succeeds, a rehearsal perhaps for reaching her ultimate goal.
But why a crow? Haruko's (some say corny) speech at the end should give us a clue. Humans cannot fly in the sky, but birds can. After Misuzu reaches her goal, Sora flies away to find the girl in the sky who's still alone to bring her back for a new beginning.
What is the use of wings which cannot flap nor fly?
It's to remind us of those happy memories from when we could fly.
What is the use of friends or family who ultimately die or leave?
The happy memories they leave behind.
Uraha is not Misuzu's mother. They aren't even related.
Ryuuyu, not Yukito, was Uraha's companion. Their bond to Kanna was as a family. They would do anything, even give their own lives for Kanna's happiness.
Yukito turned into a crow but he never left Misuzu. He's in every scene from his transformation until the end.
Don't confuse the series with the movie. Similar themes but different story. The movie jettisoned a lot of the mystical elements that were in the series other than the legend (soap opera) of Kanna and Ryuuyu and...
The bit at the end where Yukito's doll leads him to Misuzu and then bounces into a feather and disapears. The connection between Kanna and Misuzu, Yukito and Ryuuyu is more thematic than literal in the movie. At least that's how I saw it.
I enjoyed both the series and the movie, but the series is far superior in my view.
As for the two kids at the end, Misuzu dies and her soul returns to the sky but this time with happy memories she got from having spent the time with her mother. There's a bit more to it though. There's debate as to whether or not the two kids seen in the ending were yukito and misuzu reincarnated. Nobody really knows. They represent "a new beginning".
I hope this was helpful to someone even though it was a bit long-winded.
(Credit goes to an unknown poster on Animesuki. I added my own insights where I felt they'd clarify, but the main body is his)