Karakal Hot Zone 120 strings. So hot they appear to be literally on fire!
They come in different colors. Black:
Thanks to Nick for mentioning this string:
Could you add a post for Karakal Hot Zone 120 strings?
They come as standard in all of the high performance Karakal rackets, and seem to have decent performance.
Also used by Tesni Evans – https://www.string-doctor.com/single-post/2018/07/30/What-the-Pro%E2%80%99s-Use-Tesni-Evans-World-No-12