A fairly generic story about a guy who isn't even technically a necromancer. Tower appears and people who climb it become gods. A human tries it and is betrayed. Luckily, he got the ability to be reborn from a hate-friendship with a "god". So he climbs the tower again to seek revenge and soon finds out that the 4 strongest races of the tower are behind his death - so a few more people on the "they must die" list. As I said, a very generic and therefore almost dull story. Strong guy, reborn and wants revenge - there are stories like this a dime a dozenand "All-Master Necromancer" or "Absolute Necromancer" doesn't do anything special with it. If you set up a bingo card with generic manga tropes, you'd have bingo in 5 chapters: asshole protagonist? Yup. Harem? Yup. Op? Yup. etc.