The one by Shindo L? I remember skimming through it when I was 16, but I never fully read it I would just skip to the part where the mc was pregnant (<- guy who has fictional pregnancy kink) I might’ve read some of Shindo L’s other works, but I could probably give metamorphosis another go! I rarely read manga but one I really like is Kasane by Daruma Matsuura. I never finished it though I only read to around vol 4 but I LOVEEE the art style, those manga covers are UUGH 😩🙏💕 they def inspired me artistically. If you’re interested in psychological horror then check that out!