More information:
http://forums.animesuki.com/showpost.php?p=5831196&postcount=268
Arc 5:
http://forums.animesuki.com/showpost.php?p=5844149&postcount=389
http://forums.animesuki.com/showpost.php?p=5844216&postcount=391
Unorganized Spoilers
Satella is in love with Subaru, probably since eternity ago, and reason is unknown.
She pretty much went insane and nearly destroyed the world, and was sealed by combined efforts of Dragon, Hero, other witches, and the whole world.
Her aspect somehow affects Subaru (and likely summoned him to the world) and any time Subaru tries to tell anyone about his ability to loop, the aspect of the witch will hurt him and kill whoever he tells it to.
She's basically the reason for every goddamn mess and despair in that world. The Cult of the Witch worships Satella and is basically the world's satanists.
The seal is guarded by the Sage's Tower that kills literally anything that gets too close.
When Subaru starts getting close to it accident via underground tunnels, he and the two other people with him can't handle the miasma she releases. They go insane and start killing each other.
Emilia also immediately died when they first saw the tower and Beatrice is the only one who could avoid dying.
Once they get inside, the sage isn't even there and the caretaker is a complete dumbass that has no idea about anything ever.
Not to mention they're forced to solve puzzles. PUZZLES!
Satella has taken over Emilia's body once (part of her went through Emilia). The seal isn't as effective as people think.
When that happened, the world immediately became fucked up and ended.
On Witches:
Satella, Witch of Envy - Satella was not a vassal fit for the Witch Factor, and forcing herself to become a Witch caused her multiple personality disorder. As the evil Witch of Envy she killed and absorbed all the other six witches of Greater Sin and destroyed half the world. The combined effort of Dragon, Sword Saint, and the Sage could not kill her existence, and merely managed to seal her in the Grand Falls.
Her appearance is identical to that of Emilia. Ekidna calls Emilia the Daughter of the Witch.
Ekidna, Witch of Greed - Obsessed with knowledge, she sought to learn more even after death. After her death, her spirit was sealed by the Dragon as a countermeasure to if and when Envy awakens again. Ekidna created a virtual spirit world housed by herself and artificially recreated personalities of the other witches to hang out. She invites Subaru to this lair of witches and gives him advice on his powers. She has since become free to roam the world in a cloned body of her best friend, thanks to Subaru's actions in arc 4.
She is cunning and manipulative, and the mother of Beatrice. She is worshiped by Roswaal as well.
Minerva, Witch of Wrath - Minerva has the power to "punch" people and heal them. Her powerful punches however destroys the world at the same time. Anytime she punches people back to health, catastrophe happens elsewhere in the world. Which causes more people to become injured, and she rushes there to punch them. This infinite cycle of destruction and healing caused more harm than good, but that never stopped her from continuing.
Busty and sexy late teen with a long blond hair, Minerva is a simple and honest minded girl who speaks her thoughts out straight forwardly.
Sekhmet, Witch of Sloth - Pretty much embodiment of sloth, she is too lazy to do anything, even breathing is a bother to her. She chased away the Dragon to beyond the Great Fall just so she can have peace in her laziness.
She talks like an old crone despite looking in her late 20s.
Daphine, Witch of Gluttony - Always hungry, prefers quantity over quality. However she also suffers from eating disorders and often pukes out the food she ate. In order to end hunger in the world she created monsters such as White Whale and White Rabbits, although they ended up being just as much of a threat. Loli.
Typhon, Witch of Pride - Innocent and unforgiving loli. She punishes evil doers without mercy, and was feared for her extreme prejudice to evil.
Camille, Witch of Lust - A very average looking girl with no exceptional beauty, but her power as Lust captivates anyone who gazes upon her. Her power to be loved was so strong, most who gazed upon her cannot focus on anything else, and everything becomes meaningless to them. Even breathing or beating their hearts. They end up dying with happiness engraved on their face.
Pandora, Witch of Vainglory - Mysterious woman clad only in a single sheet of white cloth, she seems to be leading the Cult of the Witch. She has the power to "rewrite" reality of any immediate events, making her seem invincible. Definitely evil, as she brings doom and misery in her arrogance. She is likely still alive to this day and pulling strings.
Hector, Witch of Acedia - A male witch. Said to be as powerful or more than Ekidna, and controls power of gravity. For some mysterious reason his existence is not told in history.
No one on Subaru's side ever finds out about his ability.
However, Ekidna figures out his powers when she invited him into her dream world.
She opened up the possibly of bad ends continuing on after Subaru's death.
The witches in her world are the only ones Subaru can reveal his restart powers to since Satella's influence cannot infiltrate the place.
From what Ekidna says it seems there's two sides to Satella.
It seems her nature as Witch of a Great Sin basically caused her to turn into the horrible incarnation of Envy.
The other witches loved Satella, but hated the "Witch of Envy".
The aspect of Satella pays him visit regularly, usually when she's about to do something horrible to him.
Any act of trying to convey his ability, even to himself, results in yandere alone time with her.
There was one time he forces himself to tell Emilia even through the pain - the witch just brutally slaughters Emilia instead.
And when he finds a loophole in a second time that allows him to freely talk about it, it gets way worse.
Moreover, every time Subaru makes a horrible (but necessary) decision her "scent" gets stronger. He's been consuming ability of the Cult leaders, and his bond to the Witch is getting stronger.
He realizes that can't be a good thing, but he keeps choosing to do so to save his friends.
On the Cult of the Witch:
The Cult of the Witch priests take up the Great Sins, though they're basically just artificial personas of the witches in life.
They worship Satella, but despise the other witches. Their goal is to use Emilia as the Witch's vessel.
Betelgeuse Romanée-Conti, Bishop of Sloth - A spirit demon that lives since the era of the Witches. He used to be a reasonable moderate and father figure to Emilia, but was driven insane by Pandora.
Despite being the Bishop of Sloth, he actually hates laziness and constantly accuses others of being lazy and works his ass off for his zealous cause. As a spirit demon he takes over bodies to live on, and as a Bishop of Sloth he has the power to manifest the "Invisible Hands". These hands have an extremely far reach, strong enough to rip through trees with ease, and can pass through anything the user doesn't wish to be touched.
Not only is he capable of summoning a hundred of these, but he can also release a wave of miasma that renders people immobile. An incredibly powerful being, he managed to kill all of Subaru's allies in arc 3 several times. In the end, he was killed by Subaru and had his Bishop powers absorbed.
Rai Baten Kaitos, Bishop of Gluttony
Roy Alphard, Bishop of Gluttony
Rui Arneb, Bishop of Gluttony - There are at least three bishops of Gluttony, with each representing different obsession involving consumption.
The power of Gluttony has two steps: by eating the victim's "name" they can erase their existence from the rest of the world, and no one will remember who you are; by eating the victim's "memory" the victim loses memory of who they are. If both "name" and "memory" are eaten, the victim also goes into a coma.
In act 3 Cruche has had her memory eaten, and in act 5 Julius had his name eaten. Rem had both her name and memory eaten and now is a comatose with no one remembering who she is.
Regulus Cornius, Bishop of Greed - Obnoxious, whiny, and arrogant, Regulus never shuts up. He constantly justifies his own action and complains about everyone else's. He is easily enraged and throws tantrums if anything or anyone doesn't act the way he wants them to. Regulus also forces women he finds to his liking to become his wife, and has dozens at any time.
He has two powers as the Bishop of Greed, which compliments each other: "Time stop" and "the Small King".
He can stop time of his own body or anything he touches, making it invincible. However using time stop also stops his own heart, so this ability is unusable by itself. "The small King" allows him to superimpose his own heart on someone else's, allowing him to have a beating heart even while his own is stopped. You'd have to kill that other person, or remove Regulus' heart from him/her first to inflict any damage.
"Time stop" was also his primary method of attack - he would use his foot like a shovel and kick dirt or mud or whatever at people, and due to the object's time being stopped, it would become basically an unblockable attack and would cut through things like butter.
When Subaru and co. fought against Greed, Emilia first removed the fake hearts from his wives' bodies by putting their bodies in cryostasis with ice magic. After the heart moved to Emilia. Subaru's "invisible hand" ability becomes useful for the first time as it's used to remove the fake heart from her body.
Regulus was killed by Subaru and Reinhart in act 5, and had his Bishop ability absorbed.
Sirius Romanée-Conti, Bishop of Wrath - Self-claimed wife of Betelgeuse. Like her husband, she is completely insane.
She controls flames and fights using chains wrapped around her.
Her fighting ability is very strong, enough to fight against Reinhart for a short while.
Her ability as Bishop of Wrath is to impose her own emotions to others in a large radius, turning them into her puppets.
Even worse, any damage she receives becomes imposed on everyone she controls, thus hurting her results in mass death of civilians around her.
Capella Emerada Rugunika, Bishop of Lust - Possibly the biggest piece of shit in the cult.
Most bishops while insane, follow some type of belief. But Capella seems to be sane, just completely vile and evil.
She wants the whole world to love her and only her. She enjoys shitting on people's pride and values by toying with them.
Her power as a Bishop is shapeshifting, both herself and others. Capella turned all her hostages into giant flies.
She either takes a form that's attractive to her victim, or a form that's powerful such as a Black Dragon.
Capella's true form is unknown, but she seems to be at least part dragon.
Her dark dragon blood invaded Subaru's body, causing his body parts to turn pitch black.
They are apparently toxic to most, as Cruche suffered massive pain by being inflicted by it.
Subaru managed to kill the Bishops of Sloth and Greed, and was forced to absorb their disgusting Sloth and Greed essences. No, they don't really help all that much.
He gets them because he's a compatible vessel and the essence holder dies near him.
For example, he kills Sloth via road kill and gets the essence that way.
However, Reinhardt is the one who kills Greed, but Subaru gets it anyway because he was simply close by and Reinhardt can't be a vessel for it.
Several people want him to gather all the essences and become a sage, whatever that means. Beatrice is against it, though Subaru himself doesn't know about any sage bullshit.