Other characters there a several characters that interact here and then with the MC I would say they are built okay nothing special. The 'Harem' has actually personality and is not like puppets every girl has his own story some backgrounds are not so well written as the others but it's still good. The world-building is great although I think the author introduced some areas too early since there is no interaction with them until like 100 chapters later or more. Even with his higher power level he is not so s*upid and thinks he can defeat anything well 'worthly' opponents are most like not humans they are demons or evil gods etc.
His personality is not the Typical Good boy MC he is neither bad nor good he slaughters without problem thousands of people without worrying much. First the MC if you like OP mc's that the novel is for you, in the beginning, he was really weak and nearly died several times but he worked hard under his Master to achieve a unique Spearmaster class and he still grows my personal opinion he is already like a Demigod or low-level god in terms of raw power.