This is a good explanation but quite confusing. Please don't mind me and give me the honor of explaining on your behalf...
Ria's brother died and he wanted him to come back from the dead (creating a substitute). But before that, he made Ritz (did I got the name right). Ritz was an incomplete one, a prototype.
Ria died without having to create a definite result, that's why he entrusted his will and researches to Ritz.
So, Ritz finished the project, successfully.
Sad and beautiful
Loop (so-sol) Manhwa