I don't think there's a good answer as to what Miku and Itsuki hair "loop(s)" here can be called. I thought they may be hair rings but that tag seems to be for "loops" that are much smaller and relatively tighter. Sidelocks tied back actually seems more in line with what the hairstyle can be called but in Miku and Itsuki cases, they are not sidelocks.
My suggestion would be making a tag called "bangs tied back" to describe both Miku and Itsuki hairstyle. Also, although the wiki for sidelocks tied back consideres Bunker Hill (Azur Lane) to be an example, I think she fits the suggested new tag better.
If anyone can tell me a better tag for the mentioned Nakano sisters, I'll appreciate it. If not, I'll go ahead and create the new tag.
Edit: I seriously forgot to include post #7500028 as example. My bad.
Updated