What was unlawful about your demotion? Most US employees can be demoted for no reason, or have their salaries docked arbitrarily.
The commenter is probably employed in a jurisdiction that is not the US.
A quick examination of their post history yields a description [1] of employment in a jurisdiction that is not the US.
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Labor law supersedes the contract freedom guaranteed by the civil code here in JP. And the conditions for demotion are strict here, e.g. maximum ~40 % reduction of salary, new role must be related to previous role, etc.
The burden of evidence lies with the employer, but some try to construct a fictitious narrative. Nothing that holds up in a court of law if you remember to CYA.
It’s especially frustrating if your visa is tied to doing a certain type of job and having a certain amount of salary!
The word unlawful I am using here is 不法 (fuhō) in Japanese which I believe is used a lot in tort law.
Either way, long story short, there is no at-will employment in Japan.
Constructive termination + a reasonable payout to help you adjust to life post-job/divorce.
Constructive termination doesn’t get you money on its own, it just is a way to make a claim for things you would have been owed if you were fired (including wrongful termination damages, if you can also prove that the termination was wrongful) when the employer tried to characterize the termination as voluntary on your part.