I recommend a novel called "The Chosen One of the Heavenly Dao." The male protagonist was called Chen Changsheng. His father was a member of the mayfly world, his mother was a member of the Seven Kingdoms, and he also had the blood of the mayflies and the blood of the Seven Kingdoms. In this novel, there are mayfly realms and other realms. After fusing, you can ascend to the upper realm. It suits your needs very well. I hope you like my recommendation. Muah ~