There are three SINS decks in the series: SINS Mentis is based on the Sins who influence thought, SINS Corpus on the Sins who influence the body.
SINS's story is inspired by the Original Sin and the Seven Deadly sins.
Adam, the first man, and Eve, the first woman, lived in Eden. They had just one rule: don't eat the Apple of Knowledge. Prometheus, the Snake, told Eve that the fruit would gave her the freedom, and she and Adam ate it. They were banned from Eden: mortals, frail, naked - but definitely humans. Was the Snake an enemy?
The courts represent the seven deadly sins: In SINS Mentis, there is Greed (Diamonds), Envy (Clubs), Pride (Spades) and Lust (Hearts). In SINS Corpus, there is Wrath (Diamonds), Gluttony (Clubs), Sloth (Spades) and Lust (Hearts).
SINS Playing Cards are highly detailed, and are full of hidden meanings and symbiology. The three decks also represent the philosophy behind the name Thirdway Industries: thesis, antithesis, synthesis.
The backs of SINS represent Eden, the place where the first Sin occurred.
In SINS Mentis, Eve was planning to eat the Apple of Knowledge, but she didn't actually do that - so Eden was bright.
In SINS Corpus, Eve ate the Apple and she was banned. Without her and Adam, an eternal night fell on Eden. This means, chronologically, that SINS Corpus happened after SINS Mentis.