Charon

Charon (Japanese: カロン) is a minor character in Historiē. He was introduced to be Eumenes' slave in Chapter 6: The Library Room (2), who accompanied him to the school.

When Eumenes met him once more in Chapter 85, Charon was known as Melanthios, a trusted friend to Phocion. He married a former slave during his time as a free man. He still called Eumenes as young master as he felt that it is more natural to address the young man.

Just as they seperated once more, he stated the main reason why he does not have any children as he has one. One that is freed from the chains of slavery just like him. No matter what he does, like attacking Athens, he considered Eumenes as his only son.
(Source: Historie Wiki)