The Culprit

'Good,' Gustav said internally with a sigh of relief.

Gustav already knew why they came to draw his blood amongst many others that were here. 

He could tell that they had already seen footage of where he dealt with the infected and they already suspected he was immune.

The problem was, that they still wouldn't be able to create a cure from his blood because Toxin Immunity was a system-based ability.

If it was a bloodline-based ability, his blood would most likely have an effect and might be of help. Gustav had asked the system to contaminate his bloodline since they would be conducting examinations on it.

It would be suspicious if Gustav forcefully refused them so this was the best course of action to prevent them from figuring out secrets from his blood or using it for any other purposes.

[God Eyes Has Been Activated]