Pastlives
Fang Yuan is a character obsessed with Immortality, and to achieve it he will do everything he can to achieve it, he is a reincarnated person who came to a world of Cultivation centered on Insects that give Abilities to their users. As for Klein, I didn't understand the comparison, he is Chinese who did a ritual where he went "isekai" to another world, his personality is good he wouldn't torture someone out of pure curiosity about something
Wang Lin is someone who quite literally had to face the cruelty of the cultivation world at a very young age and had his innocence crushed with a metaphorical sledgehammer. The only thing in common between these mc's is their profound distrust and increasingly cautious behavior that often puts batman to shame. But other than that it is difficult to compare them as Wang Lin quite literally lost everyone he had ever cared about and thus his extreme lack of empathy was natural as he lacked prominent social interaction due to the nature of his world. Fang Yuan is more or less same as him I guess with his ambition becoming his motivation to live. Klein is vastly different in nature due to his environment which shaped him. Despite his distrustful nature mirroring the above two he never truly lost his drive or neglect his humanity but rather embraced it to keep himself sane. Main reason for this is due to his environment he was never truly 'alone' due to his allies, mentors and members of the Tarot club forming a sort of indirect emotional support that kept him from becoming a brutal out of control monster. Even at the end his sacrifice was driven by his desire to protect his 'family' and 'friends' from a fate worse than death, while not explicitly stated his heroism was in fact an innate instinct to protect his loved ones and the rest of the world was just a tag along in this case. It would be unfair to compare the different mc's as WL quite literally never had many 'bonds' to speak of because the nature of his world and its people wouldn't let him form them and neither could he do so if he wished to survive and thrive.
Wang Lin appeared as a simple village boy, he took the path of cultivation in order to fulfill his parents' hopes, as a village boy he had no thoughts of committing murder, but a series of events forced him to do this until he killed the descendants of strong cultivators which resulted in the death of his family and himself. However, thanks to the sacrifice of those closest to him, Wang Lin was able to rise again, this is where Wang Lin began to do everything he could to gain strength so that his revenge could be achieved. When his revenge was achieved, Wang Lin experienced a change in desire to achieve enough strength to survive and live in peace, until the death of his partner according to the destiny given by Heaven, Wang Lin was very against it, he waged war against Heaven to seize his partner's soul. He was the Renegade Immortal, Wang Lin. Google Translate