Quick Transmigration: Villain, Please Don't Go OOC

[Dual Male Leads, Quick Transmigration]

After Gu Tian died, he unexpectedly obtained a System. With the System's training, he became nearly all-around capable and even successfully bound himself to a Villain System.

It's just that...

Gu Tian hadn't expected that the protagonists in every world would all have extraordinary identities. Some were hidden big shots, while others were simply there for revenge.

He had to complete his missions while maintaining his persona and avoiding going OOC.

But what on earth was this mechanic where reaching max favorability lifted the OOC restriction?