People need to stop over-analyzing the wholesome and sweet story about newly-met newlyweds and just enjoy the fluff. The mysteries will come later, and they are not sinister. The only thing sinister is an obsessed 'adoptive' sibling of Tsukasa's who is honestly pretty ineffective because Tsukasa can see right through her schemes. Tsukasa herself is very earnest in the relationship, she's just got a better handle on her mental state than you'd expect from a 16 year old because she's actually been around for a lot longer than 16 years.