So, Samuel is 100% a child. The ending clearly points towards a romantic relationship, even if the author says that Samuel didn't confess his love.
You could make the argument that since Noir / Lich Quing died while a child, then spent the rest of their life in relative seclusion, that they have the maturity level of a child. Which would make it kind of better, but still very creepy to be glorifying it in this story with such a seemingly happy ending.
Overall pretty off-putting story, though I like the style of the art and designs. Also the "Quing" scene was a pretty cute way of getting across the character's identity without making a big thing out of it.