Why is Tsukushi so absurdly gullible? Well...would you tell an extremely bossy and violent track team captain, practically a female Drill Sergeant Nasty, that she's wrong about something? Everyone is afraid to question anything she says or does, so there's no one to stop her from developing Cloud Cuckoo Lander symptoms.
The reason Tsukushi believes so strongly about "younger Yokodera" is not only because of her status as a Cloudcuckoolander, its also because, due the Stable Time Loop, she vaguely remembers seeing two Yokoderas at the same time during her childhood.
