@Triot nah, the "13 year old" figure for Japan age of consent is old and not used as each municipality and prefecture in Japan has their own law for this: Tokyo is 18 years old
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also no the ppl calling for romance -_-
koto has serious issues and mental health problems from her situation at home and her father being gone. Ignoring what she's doing, the actual goal of said actions is a cry for help: she's looking for a father figure to fill the void, cause of how her mother treats her. The MC is that person cause he's the one who actually showed some care to her, and she latched onto that hard cause she's desperate for help and MC = father figure
MC needs to get her real professional help with a therapist as well as getting her away from the stupid mother. Koto's talk of "I want sex/relationship" is her trying the extreme to get the MC's attention as well as her possible misguided view that only those would give her the protection/attention/care/affection that she desperately needs... in reality, actual sex would be something she'd regret for the rest of her life and would not her help at all as it wouldn't be addressing her fundamental issues and mental health