What are the main risks or side effects of nattokinase, especially with blood thinners?

The short version: the evidence retrieved does not contain a single study on nattokinase, so the question cannot be answered from the provided material.

The evidence block you supplied is empty. There are no studies, no case reports, no mechanistic data, and no safety analyses to review. Without any retrieved evidence, I cannot name a risk, cite a bleeding rate, or compare nattokinase to a blood thinner. The gap itself matters: the absence of retrieved evidence means the question is unanswerable from this source material.

My call: the evidence retrieved does not address this question. Confidence: not applicable — no evidence to evaluate.