But if I list the betrayals, it'll spoil it, right? Here are some anime full of betrayals, anyway, so you can enjoy them for yourself. I'm afraid I don't usually read manga I haven't also seen the anime of.
Phantom: Requiem to the Phantom - A young man with no memories fights to salvage his humanity when he's forced into a life of murder by a dangerous crime syndicate called Inferno. The organization gives him a new name, Zwei, and molds him into a perfect killing machine, a meticulous instrument of death created to obey his masters' every deadly command. Zwei's not the only puppet controlled by Inferno; Ein is a girl as beautiful as she is brutal and as lethal as she is lost. While mafia violence escalates around them, the two assassins grow closer, and Zwei begins the struggle to reclaim his past and save Ein from a blood-soaked future.
Gungrave - For Brandon Heat, death doesn't matter. Driven by his need for revenge, he returns from beyond the grave to cripple Milleneon, the huge mafia organization which uses undead monsters as its enforcers. His ultimate goal is to destroy Harry MacDowel, the leader of Milleneon and, at one time, Brandon's best friend...
When They Cry - It's hard enough moving to a town where everyone has known each other their entire lives. Ever since Keiichi arrived in the picturesque town of Hinamizawa, he keeps discovering ominous happenings that don't make any sense. Unsolved murders. Disappearances. Mutilations. The worst part is that he can't be sure whether or not his new friends like Rena, Mion, Satoko, and Rika are aware of the events or involved in what's happening. All he knows is that it's not paranoia if someone really is trying to kill him, and escaping Hinamizawa alive may no longer be an option.
Basilisk - Reared from birth as sworn enemies, the ill-fated lovers Gennosuke and Oboro seek lasting peace between their peoples. But war ravages their rival clans, and two lists seal their destinies–two lists from which a name can only be crossed out in blood.
Death Parade - Decim is the lone bartender of the Quindecim bar, but his true profession is an arbiter--a judge of where one’s soul is sent after death. Souls sent to Quindecim must be judged through the Death Games: seemingly simple bar games with sadistic twists. To Decim, judgment is easy, until he meets a mysterious black-haired young woman whose fate seems impossible to arbitrate.
Code Geass: Lelouch of the Rebellion - In 2017, parts of the world are under the control of the Holy Britannian Empire. Japan is now known as Area 11, the proud people treated as lower class citizens. Lelouch Lamperouge was once a Britannian prince but when his mother was assassinated, he was left in Japan and thought to be dead.
After getting caught up in a terrorist attack, he encounters a strange girl known as C.C., who grants him the power of Geass and the ability to command others. With his newfound powers, Lelouch becomes Zero, a rebel leader for justice, and forms his own anti-government group. His goals are simple: get answers about his mother's murder and make a world that is worthy of his beloved little sister, Nunnally. Even with his Geass, Lelouch will encounter countless challenges. But nothing can prepare him to face his former best friend, Sazaku Kururugi, a Japanese citizen...and soldier of Britannia? The power of Geass: Is it a blessing...or a curse?
Shiki - Encased by trees that are used to make grave markers, Sotoba is a village thought to be surrounded by death - a fact that soon literally becomes the case. One summer, a series of mysterious and untimely fatalities begins to plague the small rural town. With a higher than normal mortality rate for the time of year and each cause of passing remaining unknown, Toshio, the local doctor, and Seishin the temple’s vice chief monk become suspicious and take it upon themselves to investigate. However, as the deaths begin to pile up, more people begin to wonder just what is behind this sudden epidemic; could it have anything to do with the bizarre Kirishiki family that recently moved to the village?
Ayakashi Japanese Classic Horror - the Goblin Cat Arc - In feudal Japan, evil spirits known as mononoke plague both households and the countryside, leaving a trail of fear in their wake. One mysterious person has the power to slay the mononoke where they stand; he is known only as the Medicine Seller, and he vanquishes the spirits using the power of his Exorcism Sword. However, in order to draw his sword he must first understand the Form, Truth and Reason of the mononoke. Armed with a sharp wit and keen intellect, the Medicine Seller wanders from place to place, striking down the evil spirits in his wake.
Monster - Dr Kenzo Tenma is a genius surgeon working in post-Cold War Germany who has a bright future ahead of him. He is admired by his colleagues, loved by his patients, and due to marry his boss' daughter, the beautiful Eva Heinemann. One day, when two patients in desperate need of emergency surgery are wheeled into his hospital, Tenma faces a terrible choice of saving the orphaned boy who came first or the mayor of Düsseldorf, whose recovery would raise the hospital's profile and boost his own career. Against the demands of his superior, Tenma does what he believes is right and saves the child. However, his decision not only damages his prospects, but unleashes a chain of events so horrific that it might have come from the depths of his worst nightmares. Laden with guilt, Tenma begins a journey across Germany in search of a formidable young man who will challenge his morals, his love for life, and his very sanity.
Rokka: Braves of the Six Flowers - Legend says when the Demon God awakens from the deepest of darkness, the Goddess of Fate will summon Six Braves and grand them with the power to save the world. Adlet, who claims to be the strongest man in the world, is chosen as one of the "Braves of the Six Flowers" and sets out on a battle to prevent the resurrection of the Demon God. However, it turns out that there are Seven Braves who gathered at the promised land…
The Seven Braves realize there must be one enemy among themselves, and feelings of suspicion spread through the group - with Adlet being suspected first and foremost.
I took the summaries either from the dvd backs or from anime-planet.