Angel Sanctuary

It's a Kaori Yuki manga. This is all you need to know.

A tale of a boy named Setsuna Mudo, a Troubled but Cute high school student who also happens to be the reincarnated fallen angel Alexiel. Now he's gotten himself in the middle of a war between heaven and hell; only this time, it's the soldiers of heaven who are evil unholy bastards.

But this of course, is only the Backstory. The real plot is that Setsuna wants to get in his (biological) sister's pants.

At least, that's the case for the anime and the first arc of the manga. Things go on much longer in the manga, and ultimately become quite complicated and aggressively bizarre. Mutated fetuses try to destroy the universe towards the end.

Has a series of drama CDs, which is based on several manga arcs.

Tropes used in Angel Sanctuary:

 * AI Is a Crapshoot:
 * All Love Is Unrequited: Or ends badly.
 * Always Save the Girl: Played straight at first, then subverted: The first time Setsuna reaches Sara, she refuses to go with him, since it would trigger widespread consequences.
 * Ambiguous Gender: Belial made a decision when she was an angel to be genderless. Since it was decreed by God that angels must have a sex, the result didn't quite work out as intended.
 * Anyone Can Die
 * Attempted Rape: Astaroth threatens to rape Kurai, but he gets stopped by Astarte taking over his body. Early on in the manga, Sara has a flashback of Setsuna protecting her from this as a child.
 * Ax Crazy: Rosiel, oh Rosiel...
 * Becoming the Mask
 * Beauty Equals Goodness: Deconstructed. Viciously.
 * Bishonen: Too many to count.
 * Bishoujo: Not as many as bishounen, but there are several. Most notably Alexiel and Jibril.
 * Black and Grey Morality: Sets up and subverts God Is Evil and Satan Is Good; nobody is really that wonderful but almost everyone has an understandable, if Wangsty, reason for what they do.
 * Except God himself. Every single conflict in the series arises because God is a complete and total bastard.
 * Blessed With Suck: Another recurring theme. Most characters with unusual power or beauty end up paying pretty damn hard for it, directly or indirectly. And some of them don't even deserve it.
 * Body Horror: Plenty of examples, mostly provided by Rosiel.
 * Brother Sister Incest: It is even relevant to the plot. Unlike many similar situations, Setsuna and Sara.
 * Councilof Angels. And boy are they bastards.
 * Dark Is Not Evil
 * Death By Sex
 * Defrosting Ice Queen: Alexiel's process of re-humanization. Lucifer's too, to an extent.
 * Demonic Possession
 * Deus Ex Machina: The final episode of the OVA.
 * Dude Looks Like a Lady: Rosiel, Arachne, Astaroth... Kaori Yuki seems to love this trope.
 * To give a specific instance, when some mooks wanted to kidnap him in the middle of the night, Rosiel was able to convince them that he was woman just by talking in falsetto. The mook's reasoning is paraphrased as thus: she was way too pretty to be a man and so hence, is not Rosiel.
 * Dying Moment of Awesome:
 * Empathic Weapon: An interesting double case. Alexiel's sword, Nanatsusaya, houses a spirit which serves and follows her because she knows his real identity . On one of their adventures, said spirit's human form finds a katana with spiritual powers and sentience, which asks him to follow him around. So, the mystic sword's personified spirit can now summon a mystic sword of his own. Is that a good weapon or what?
 * Even the Girls Want Her: Alexiel and.
 * Fate Worse Than Death: No, not being caught in a some endless cycle of reincarnation of cruel lives and brutal deaths, each time.
 * Rosiel didn't have it easy either. Seems that God enjoyed torturing his closest family the most.
 * Fetus Terrible: Sandalphon
 * Healing Factor: Kira, although his recovery rate gets increasingly slower as the series progresses. Also Alexiel and Rosiel.
 * Healing Hands: Raphael
 * Heroic Sacrifice: More than enough, but most notably.
 * Heterosexual Life Partners: Raphael and Michael, Setsuna and Kira.
 * He Who Fights Monsters:
 * Impossibly Cool Clothes: Particularly in the manga.
 * Kavorka Man: Raphael
 * Lady of War: Alexiel
 * Light Is Not Good: Nope. Not at all. Conversely, Dark Is Not Evil. Hell, one of the most sympathetic groups in the manga are a race of underdog demons called the 'Evils'.
 * Loads and Loads of Characters: If you use all your fingers and toes you may count the REALLY important ones.
 * Lotus Eater Machine: Setsuna gets trapped in very early in the manga. In this dream, Sara is not his sister, but his girlfriend, he is a normal teenager, and the guys who died in the first volumes are alive and well.
 * Murder the Hypotenuse: Laila set up her rival to be killed by their loved one. Which he regrets all of his life.
 * My Sibling Will Livethrough Me
 * Names to Know In Anime: The drama CD cast is somewhat stellar. First off, Takehito Koyasu as Kira.
 * Not Blood Siblings: Subverted even before the series got going. One of the first scenes in the OVA is Setsuna resigning himself to the fact that he and Sara are related.
 * No Womans Land: Heaven is this. While most men there do not have it easy, women have it worse.
 * Person of Mass Destruction: The Archangels, Alexiel, Rosiel, Lucifer...
 * Pieta Plagiarism
 * Playing Against Type: A drama CD example - Show Hayami voicing the heroic and somewhat emo Uriel.
 * Reincarnation: Obviously.
 * Respawn Point / Body Surf: Lucifer, willingly and unwillingly.
 * Screw Destiny:
 * Sharing a Body: Alexiel/Setsuna, Lucifer/Kira, Jibril/Sara - though this also ties in with Reincarnation.
 * Shout Out: Tokyo is destroyed on July X, 1999.
 * Setsuna speaks of the Ladyhawke movie, unknowingly speaking about.
 * Smoking Is Cool: Most notably Kira and Kato.
 * Star Crossed Lovers
 * Sugar and Ice Personality: Kira. But Alexiel and Lucifer are extreme examples too.
 * The Beautiful Elite: And how!
 * The Chessmaster Rosiel and.
 * Tsundere: Kurai and Anael.
 * Tragic Monster: Where do we even begin?
 * Transsexual: Arachne. In his case, he doesn't have reassignment surgery because it'd mean he would lose some of his strength.
 * Was It All a Lie
 * White Haired Pretty Boy: Rosiel
 * Winged Humanoid: Almost everyone, which is not surprising. Some characters have unusual numbers. Adam Kadamon has 6 wings, Rosiel and Alexiel have 3, and Lucifer has four. This is supposed to be a sign of their power.
 * In angelology, some of the higher castes of angels are supposed to have more wings than the lower castes. The idea is overall sound, but it isn't actually accurate. Assuming you believe the really straight angelology stance on this, Lucifer should have 6 wings because he was a Seraphim.
 * Woobie Destroyer of Worlds: Setsuna and.
 * Yandere: Rosiel. Uriel used to be one.
 * In angelology, some of the higher castes of angels are supposed to have more wings than the lower castes. The idea is overall sound, but it isn't actually accurate. Assuming you believe the really straight angelology stance on this, Lucifer should have 6 wings because he was a Seraphim.
 * Woobie Destroyer of Worlds: Setsuna and.
 * Yandere: Rosiel. Uriel used to be one.