A lot of animes flop so badly

What matters is if the ending fits or seems earned.
Did the events leading up to feel like they were leading up to it? Is the ending the result of one skrew up or an unavoidable outcome? These are the things I strive to achieve as a comic creator

My manga idea is a cosmic horror seinen disguised as a shonen where the main character kills himself and turns himself into an omniverse where the planets are made of blood and bone and the stars are ignited flesh, that's obviously the ending bc why would any story that isn't an issekai start with the MC killing himself?