Ending Aversion: The ending upset a lot of different fan factions for different reasons:
The people who were reading for the mystery arc thought that the final explanation was simply too silly and bizarre.
The shippers were unhappy that Mashiro and Sou end up in the real world but with no knowledge of each other or memory of their love.
The people who were reading for the exploration of ambiguous gender thought that the revelation that Mashiro's gender ambiguity is because they are actually fraternal twin foetuses sharing a mind meant that the situation was either reactionary or too fantastic to have any real-world relevance.
Ho Yay: Between Sou and Mashiro, who doesn't belong to either sex but identifies as male. Sometimes. That's sort of the entire point of Mashiro's journey. And by the end, Mashiro identifies as female, full stop.