So I was bored a few days ago and compiled some things I noticed about each Sin, and I wanted to share it with everyone here. If you have anything to add, feel free to reply! :)
Anyway, here it is:
LUST is a selfish desire, a feeling that everyone around you is merely a source of your pleasure. Take Duke Venomania, who defiled countless women to the point of even raping old nuns and little children! Asmodean is inspired by the Arabian peninsula, where misogyny is at its peak, if I'm not mistaken. There, women are treated almost equally as livestock!
GLUTTONY is animalistic hunger, and basically being batshit insane. Take all of the reincarnations of Gretel - Wicked Maid, Ney Futapie, and the female Servant - they're all axe crazy, bloodthirsty, macabre souls! Gluttony also has a strong connection to death. Gluttony's original form, a pomegranate seed, is reminiscent of the seeds Persephone ate while in the underworld! Ney, wielding the Glass of Conchita, was able to resurrect a bunch of dead soldiers and turn them into a zombie army. Conchita herself drifted between life and death for three days, and the Master of the Graveyard is often called the "Queen of the Dead"! Also, Beelzenia has numerous graveyards for those infected with the Goula disease, which is inspired by the real-life disease tuberculosis, which is interestingly nicknamed "consumption"! Hansel and Gretel also have heavy ties with Gluttony. Aside from being Conchita's servants in their future reincarnation, they were abandoned because of a famine and pushed their false mother into an oven, where food is cooked. The ocean also tends to engulf (or "eat") whatever goes into it, making it befitting that a contract with the Demon of Gluttony involves writing your wish on paper, putting it in a bottle, and throwing it out to sea, as if "submitting" it to the Demon of Gluttony! Gluttony also seems to have a "parts of a whole" kind of theme. Take the Glass of Conchita, which contains Hansel and Gretel's souls instead of just Conchita's! Also, the Beelzenian Empire once had two countries as its territories before they broke off. Beelzenia is inspired by the Roman Empire. Romans had this practice where they would lie down on sofas around a large table, eat until they were sick, barf it all out, and eat some more
PRIDE has a double connotation, just like the Kagamine twins. The negative pride is narcissism and self-centeredness, while the positive pride is patriotism and to some extent loyalty. Therefore, the sin of Pride is "split up" between Riliane and Allen, the princess and her servant. Their punishment is separation, as one can plainly see! They both suffered for their sins - Riliane living her life full of guilt and Allen being trapped in "purgatory" for almost half a century! As you can see, Rin characters all throughout Evillious are often separated from their counterparts. Take The Composer, the mysterious girl who wrote the Clockwork Lullaby. Or The Scientist (who is implied to be Gretel) in a laboratory by herself! Rindl Blume, from the Lunacy of Duke Venomania, also does not seem to have a Len counterpart! Ney was incarnated separately from Hansel, making her also technically a Rin character who was separated from her counterpart. Also, the Rin character in Pere Noel, all alone without Lemy Abelard! The punishment of Len characters is death, while the punishment for Rin characters is living without their "other half". Lucifenia is inspired by France. Before the revolution, the French monarchy was extremely corrupt, the most obvious example being Marie Antoinette. Her palace was filled with gold, which she couldn't even spare just a little bit so that the peasants outside could fill their empty stomachs. Marie Antoinette's line "Let them eat cake" was in response to a minister's report that the peasants outside could not even afford to eat bread. This shows how detached she is from the outside world and the feelings of others. Pride is also related to extravagance, given the palace of Lucifenia possessing gardens fit to be called The Heavenly Yard (just like the one in Versailles!). Riliane was also a profligate for extravagant dresses and the like.
SLOTH is outright despair, a graver version of just plain laziness. It's the complete loss of a will to live, an extreme absence of hope. Take Eve Moonlit, who was destined to be queen of the most powerful country in the world, her dreams dashed on the rocks and served with a cold side of failure. Margarita Blankenheim also despaired, thinking there was nothing she could do to repair her failing marriage with Caspar. Mikulia Greonio, to some extent, also despaired; she was born to a poor family and became a prostitute either before or after the Venomania Event. Sloth is also tied with poison, specifically how it paralyzes the body. Margarita and Margaret both died from poisoning, after all. Sloth is also associated with plants and trees, given Eldoh's forest in Elphegort (Eldoh is known to fall asleep easily, further tying him to Sloth!) Elphegort is inspired by Germany.
WRATH is revenge, retribution an justice. What makes it different from just plain Envy is that the person you're targeting actually DID something to you. We often hear the words "flames of wrath" in songs, but this is a bit of a red herring since Greed is more associated with fire. Clarith was about to murder Riliane for taking away her ONLY FRIEND. See what I'm saying here? The family Kayo killed was completely innocent, but Riliane was tainted with sin. Also, the Master of the Hellish Yard is a gatekeeper to the underworld, a concept present in many religions (and not just Christianity). If I'm not mistaken, Zoroastrianism has this concept called the Shinai Bridge, where souls cross to get to heaven. If you were righteous in your past life, the bridge became wider. If you were sinful, the bridge became narrower. The Vessel of Wrath is a Golden Key, and keys are symbols of leadership. Take St. Peter the Apostle, to whom is entrusted the keys of heaven!
ENVY is hallucination, mental obscurity, and outright delusion. Eve Moonlit, Hansel and Gretel, and Kayo Suduo were all subjected to the power of Envy at some point of their lives, but in varying extents. Elluka Clockworker is no exception to the Demon of Envy's influence. I mean, she just murdered her SISTER to be ruler of the most powerful country in the world. She also envied Kayo's beautiful figure, and switched bodies with her! Envy is also tied to themes of "opposites coming together", similar to the Taoist concept of yin and yang. The most obvious evidence of this is the Clockworker sisters, as well as the blending of red and blue in Blood-Stained Switch and Full Moon Laboratory.
GREED is material attachment to wealth. Men from Marlon, the Country of Greed, have an obsession with collecting things, notably Keel Freesis and Gallerian Marlon. Greed is heavily associated with flames and fire, given that Gallerian's house burned down, the Marlon Spoon has fire powers, and Gallerian saw blue fires in Hell. Fire consumes your body, sort of like the way Greed consumes your soul.
I'm fairly certain that your reference to the Roman practice of eating until one vomits and then eating again is false. This urban myth came from the Latin word vomitorium, which actually was just a large exit in colliseums.