I don't think it's that complex. I don't really see Tenten's "face shape" in there, nor is it really Ino's eyes. What I think is that this is something outside the Naruto universe, thus Hinata is not in her ninja clothing, she does not have the Byakuugan, and maybe that's why her personality is a little different. That little bit is not quite "Sakura's personality" either. This girl is being represented too cutely for that. I think it is meant to be Hinata--the animators wouldn't try to be so confusing like that. This is a different art style, is all, and set outside canon universe. She's just a regular girl, and if her name means "Sunny Day" well, it does stop raining and the sun comes out, thus she rides her bike.
The song is stuck in my head, and while it's a simple ending it contrasts the darkness of both the opening and the arc. It gives you hope. Push Hinata! Push up that hill!
It can't be Hinata:
A)She's completely flatchested not DD cup. With a shirt like that Hinata's breasts would look enormous (believe me, I know. I've been D cup since I was 14 and had a shirt like when I was about 17- they made my breasts look even larger than they did in other style shirts. Thus after a few times of getting way too many leers from guys, I never wore a shirt like that again. One personality point I shared with Hinata when I was a teen was major discomfort with how my big breasts drew too much attention, I hated- and still do- being the center of attention for any reason. Yes, believe it or not I'm an introvert.) Even Sakura's B cup breasts would be obvious (my younger sister had B cup breasts during one period where those type shirts were in style and even she looked busty in that type shirt) only on a flatchested girl like Karin would the shirt look like that.
B)Look at the eyes the there are whites of the eyes and significantly darker irises but no pupils like Ino's, Hinata's irises are the same color as the whites of her eyes as are her pupils- in close ups like the image where you see the girl's eyes.
C) Hinata's eye shape is more oblong than that girl's, Sakura's are that shape.
D) Hinata has a slightly rounded rectangular face, Tenten's face is shaped like the girl's.
E) The girl has an open, expressive nature like Sakura's, with a smile like Sakura's. Hinata has a inhibited nature with a only a slight hint of one when she smiles.
She's a generic Narutoverse girl. I think some fans just want it to be Hinata because the last ending was Sakura and narusaku centeric. But it's not any specific girl, it's a blend. I also agree with others that the ending theme animation is quite out of touch with the series tone at this time. It's like the animators got the anding theme mixed up with one they would have for a lighthearted younger shoujo anime series they are working on at the same time they are working on Naruto. In fact, it makes me wonder if what happened is they had this ending theme animation partly finished (notice how much more finished the nature scenes are compared to the bicycle and especially the girl) for some other series they were contracted for, but the series got canceled before the animation could be used so they quickly sketched in a generic Narutoverse girl and a bicycle and used it so the work wouldn't go to waste.
Dream you dream alone is only a dream, but dream we dream together is reality- Yoko Ono 1971
When you go to war, both sides lose totally- Yoko Ono
Remember, our hearts are one. Even when we are at war with each other, our hearts are always beating in unison- Yoko Ono 2009