Don’t forget that serial killer is completely different from some killer, they have serial in the name for a reason.
Most serial killers lack sympathy which is one of psychopath traits AKA mental disorder so yeah, you can’t just write whatever you want or romance between mc and serial killer without researching, you basically glorify mental disorder, yikes. They’re not gonna “feel that way” with just mc or have a normal cutie love life 
♀ 
Remember they lack sympathy which is one of the most important thing in romantic relationships and I doubt episode(13+) will be a good platform to write about this stuff since it’s rare to find stories that well written without glorifying