How to fight a potential paycut

Hi everyone, looking for some legal perspective and a "sanity check" on a situation I’m facing at a large tech company in Tokyo.

I’m currently at a Senior/Lead level. After a series of "calibration" reviews, I’ve been told I’m being downgraded, which comes with a 8% cut to my base salary.

The Context:

I’ve had 3 consecutive "meets most exp." ratings.

The feedback is almost entirely subjective/qualitative: "not proactive enough," "not enough influence," "not coming up with enough topics."

In fact, all my peer feedback are very positive even up to someone in a manager level who I collaborate with a lot

The only concrete "failures" they cited were two instances of "jumping the gun" on small tasks that had zero business impact. In fact I did collaborate on division-level projects that drove strong growth

The Current Situation: HR and admins are now pressuring me on Slack to sign a new employment agreement reflecting the lower grade and salary. I haven't signed anything yet. I’ve been stalling to buy time, but the pressure is ramping up.

My Understanding of the Law:

From what I’ve researched, Article 8 of the Labor Contract Act says they cannot unilaterally change my contract/salary without mutual agreement. Since this is a "disadvantageous change," I believe I have the right to refuse to sign and stay on my original contract at the higher grade.

My Questions:

Since I acknowledged the feedback documents, does that count as "tacit consent" to the pay cut? (I haven't signed the actual contract yet).

If I refuse to sign, can they fire me? My understanding is that "refusing a pay cut" is not a legal ground for dismissal in Japan.

How do people handle HR when they treat "calibration" as if it’s an absolute law that overrides an individual contract? I'm planning to tell them I won't sign and that I'm "consulting with a legal representative." Is this the right move, or will it backfire?

I’m feeling pretty disheartened because the reviews make it sound like I’m failing, but I don't want to just give away my current pay grade just to some vibe bad feedback

Any advice or experiences with labor unions (Tozen, General Union, etc.) would be greatly appreciated.

by Objective_Ask_9199