I feel like the writer just did a 180 on thebad ending even though I feel like it doesn't match the theme. I'm not a fan of bad ending myself but him going back in time feels like a dream or like just an alternate reality. Like the real story was she really died and he keeps regretting.
First of all this is not a fantasy manhwa, like everyone expected a bad ending is she would die and a good ending is she will miraculously overcome cancer. Him going back in time doesn't fit.
If its fantasy like 3rd Night Only (Sorry I can't put a spoiler tag for those whose reading 3rd Night only)
where FL died and ML turn back time, yet it's not unusual since it's fantasy and they can go back in time even before she died.
where FL died and ML turn back time, yet it's not unusual since it's fantasy and they can go back in time even before she died.