Hahahaha that girl is not some girl. That is his own right hand/right arm turn to hence the title.
C.1 p001 made me think he was complain that he could not get a girlfriend and his only comfort was his right hand (as his masturbate hand) so the "goddess" turned his right hand/arm to shape of a small breast girl.
And to C.2 his left hand/arm turns to a big boobs girl.
C.3 "the girl" he likes come to his home to check on him since he sick and not go to work. Turns out that she like him. But his "hand girls" come out and have sex with him thinking she was left but she peep on them. Pretty sure he said something that he only need them so "the girl" left with that scary/disgust face.
next chapter "the girl" must join in or there is no point of "To be continuous".
Total of 5 Chapters here. Chapter 4: https://e-hentai.org/s/241f778b88/808668-223 Chapter 5 (Final): https://e-hentai.org/s/6a0a8442cd/849814-397 Actually the main girl here, also happens to have the same powers as he is, and "took his dick" for it. But ended up going berserk. Final chapter has him making a decision to fix this by "going back to the past" and finally confesses to his love interest (the one that ended up going berserk before the fix) and correct this once and for all. Happy End in the final chapter!