Yuki Tsukumo's Cursed Technique Bombaye/Star Rage allows her to add an imaginary mass to her body, in normal circumstances, this mass doesn't affect her, meaning she can still move without being hindered. But as chapter 208 revealed, to a point, at some point the added mass actually affects her, and if she keeps adding mass she can literally turn herself into a black hole that was stated by Kenjaku to be able to destroy the Earth. However, this is a suicide attack as she herself dies from this. In chapter 208 Tengen's Barrier+Yuki's own willpower contains the blackhole while Kenjaku survives being near it by using Itadori's mom technique 'Antigravity System' to negate the intense gravitational effect of the black hole till it disappears.