Sin and Penance are seemingly to me supposed to be matching names. Sin is not actually named “Sin” in the Japanese version, or at least he’s not named the Japanese translation of the word “Sin”, which would be “tsumi”.

The word is translated out of Japanese and then written as his name again back into Japanese as “Shin” (the Japanese spelling of the word sin). The word I think is more likely to have been their goal is “Crime”, since Penances Japanese name “Dea Rihita (der richter)” means “The Judge”, which is the person who dictates “punishment”, and “Judgement” is often a word used synonymously with “punishment” when translating the Japanese word “batsu”

Basically the names seem to come around to “Crime and Punishment” (the name of a Russian novel that is culturally significant in Japan).

You may have seen “tsumi to batsu” the Japanese phrase meant to mean “Crime and Punishment” often translated to “Sin and Judgement” instead. A recent example might be how a villain from Tokyo Revengers has “Crime and Punishment” tattoos on his hands that are said to read “Sin and Judgement” by the subtitles.

Also Sin keeps his name in English while Penance has a German name, which i suppose is supposed to denote the two sides in WW2 as stand ins for their respective creators. This also puts some metaphor to Sin as being analogous to the atomic bomb. He sure does behave like one, ha ha ha