Physical Features:
He is depicted as thin and lean with pale skin and black hair, serving as a visual foil to Gozu's more muscular and "bulky" build.

Height:
He is tall, often shown to be roughly the same height as Gozu.

Age Gap:
He was 5 years older than Gozu in their previous lives.

In the modern world, he was a teacher/mentor figure to Gozu, which established their original power dynamic. 

In the game world, he takes on the role of the destined Hero who is supposed to kill the Demon King.
His presence creates a significant conflict because he still harbors feelings for Gozu, while Gozu is now completely devoted to protecting Evelogia.  

The dynamic between them is not just a battle of magic, but a battle for Gozu:

Evelogia's Resolve: Eve is deeply possessive of Gozu. Upon learning about the Hero's toxic past with Gozu and his intent to take Gozu back, Eve's goal shifts from world destruction to eliminating the Hero to protect their bond.

Gozu’s Protection: Gozu actively works to prevent the Hero from reaching Eve. He uses his knowledge of the game's mechanics to sabotage the Hero's party and ensure that the "Final Boss" (Eve) doesn't fall to the Hero's sword.  

Yes. The mystery figure with black hair (who is supposed to be the blonde Hero in the original game) is indeed related to Gozu's previous life. In the real world, Gozu was a yakuza member who was killed, but he had a complicated, toxic relationship with a man who has now also appeared in this game world. 

Key Details about the Mystery Hero:

Physical Transformation: In the original video game "World's End," the Hero is traditionally a blonde, righteous figure. However, the figure you saw in Chapter 144 (and surrounding arc) appears with black hair because he is a "reincarnator" like Gozu, retaining his real-world appearance or soul imprint.

The Connection:

This individual is Gozu's ex-lover from his past life. Their relationship in the real world was dark and obsessive, and his appearance in the game world serves as a direct threat to the peaceful (albeit villainous) life Gozu is trying to build with Evelogia.

Do they know him?

Gozu: Yes, he eventually recognizes him and is deeply disturbed by his presence, as this man represents the "social outcast" life Gozu tried to leave behind.

Evelogia: Initially, Eve does not know him, but he becomes aware of him as a rival for Gozu’s attention and a threat to their safety. 

This "Hero" character acts as a foil to Gozu; while Gozu wants to protect the "villain" (Evelogia), his ex-lover occupies the role of the "hero" but possesses the same toxic traits from their past life, making him a primary antagonist in the later chapters of the manga.

And I can't imagine Eve getting evil. The hero won't have a reason to find and kill him if he's not imfamous for being dangerous. Then why did he look for him?

 

Could it not be the hero but Gozu's ex trying to take him, because in this world the hero isn't needed. 😮 Gozu's ex as the hero reincarnated.

Or maybe it's just nothing and the hero is gonna be a new friend like the saintess.