Damn wow. This is a great twist.
And not to say I saw it coming per se, but I defo had my suspicions on unreliable narrator, albeit more in respect to Fukuishi. Her design really tipped me off to the author trying to emphasize beauty (to an arguably over the top degree), specifically from Sei's perspective. I fully expect her appearance to be different from what was shown till now, moreso than other characters at least.