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On the 2nd floor, there's a Broken Bridge that you can't cross until Cirno joins the party. If you try to cross the bridge before recruiting her, the characters will remark that they can't move on. Except Marisa, who reminds the group that they can all fly. She gets completely ignored.
On the 7th floor the party meet up with Sanae in front of the staircase leading up. Reimu, already having been attacked by Youmu and Alice in front of staircases due to them thinking that Reimu caused the incident, asked if Sanae believes the same. Sanae casually remarks that only a senile person would think that someone as lazy as Reimu would do this. Youmu and Alice are visibly shocked by this off-hand comment.