Either way chiharu is eternally suffering because she died with regrets. And hiro chan was the cause..
You’ve presented plausible theories, I think it’s a combination of A and C. What Hiro likes about Chiharu is that Chiharu likes her and thinks she’s pretty lol. I’ll bet Hiro likes that other model (she mentioned how much prettier she looks in the magazine), which is maybe another reason why she didn’t introduce Chiharu as her girlfriend. As for the end, I don’t think it was suicide. As others said, she probably fell asleep in the bathtub. Prescription sleeping meds are strong and can actually be quite dangerous, especially the side effects. Doctors don’t usually prescribe them to younger people and definitely not for “fourteen days in a row” since they’re addictive. Anyway, I agree with you, Chiharu is probably forced into this cycle of eternal suffering due to her unresolved regrets
Ps your English is pretty good, don’t worry