Please recommend me a novel where the MC is constantly changing. What i mean is that the MC continues to grow mentally as the novel progress because of their environment and the characters surrounding them. Something like Grid from Overgeared. No harem if possible but it's not a must.
Sevens, is perhaps the most obvious one in character's mental growth, but has quite an out-of-the-ordinary harem, to say it without spoiling. Kuro no Maou Martial World Talisman Emperor Spirit Realm A Record of a Mortal’s Journey to Immortality Divine Throne of Primordial Blood Ze Tian Ji.
Monster Soul Online It's the same genre as Overgeared. Unlike Grid, the MC of MSO is not greedy and selfish but too childish and naive, which can be annoying. However, like Grid, he will grow up with each increasing chapter—from dumb to naive, to pushover, to selfless, to be firm, and even sometimes sly. His growth is obvious once you read past the early chapters.