until 500~ episode it's good but after 500 episode rational though leave this novel.For example in chapter 294. demon invasion, fein kill 3 s-rank demon and his exp bar rise 3 percent. Later on witch arc he kill hundreds of S rank and at least one SS rank and it's not enough to upgrade talent.Another problem with travel, they can speed up to 15 mach speed easly but to travel 300 mile they need weeks. And writing quality drop repeat paragraph, sudden enemy appear ( in north have 30-40 s rank, and fein encounter SS rank on street and kill him and nothing happend)there is lot more, but i dont have enough english to explain