What is the bondage-like rope Yui Yuigahama from Oregairu is wearing?


I just started watching _Yahari Ore no Seishun Love Comedy wa Machigatteiru_ ,
and the black rope-like object I see on Yui looks like bondage ropes. I doubt
it really is, so what is it?

[![](https://i.stack.imgur.com/VCM72.jpg)](https://i.stack.imgur.com/VCM72.jpg)

Just watch the first episode of first season and pay attention to Yui.




I haven't been able to find an official screenshot showing this, but fan art
of Yui seems to be consistent in showing the cords being part of an undershirt
with a saw-cut edge:

[![enter image description
here](https://i.stack.imgur.com/nfIybl.png)](https://i.stack.imgur.com/nfIybl.png)
[![enter image description
here](https://i.stack.imgur.com/ZYT01m.jpg)](https://i.stack.imgur.com/ZYT01m.jpg)
[![enter image description
here](https://i.stack.imgur.com/ONVS2m.png)](https://i.stack.imgur.com/ONVS2m.png)

