Japan is at least an allied country, and they wouldn't be buying a failing company to just throw it away. The company that mainly opposed it, Cleveland cliffs wants to buy the remains to have a complete monopoly on automotive metal supply.
But part of their revised bid before Nippon included a breakup fee in case their bid got blocked on anti-trust grounds. Which, on the one hand, while I will say I probably disagree with a lot of anti-trust policy enforcement currently, the implicit notion that the rival American acquisition is better is imo kinda laughable.
The things CC is mainly interested in are like entirely horizontal, ore production/pelletizing, and automotive steel.
Cliffs has already bought AK and Arcelor's US mills in the past 5 years, the fact that they would be allowed to consolidate the midwest further is like, what do you actually believe in?