This element of surprise in anime is one of the most thrilling. 

Neglected story details suddenly make sense, and if the narrative is any good, they're left feeling as shocked as the protagonist.

The following list represent betrayals in anime that really shocked the audience.

1. Yui and Miaka (Fushigi Yuugi)

Best friends Yui and Miaka just wanted to study for their high school entrance exams.

Getting whisked away into fantasy world certainly wasn't part of the plan.

Through manipulation by Nakago, Yui comes to blame her best friend for any and all misfortune that befalls her since her entry into the book world.

Emotionally traumatized, she looks to revenge by separating Miaka and her lover, Tamahome.

It's only after her wishes almost destroy her hometown that she sees the error of her ways. 

2. Spike and Vicious (Cowboy Bebop)

The audience is introduced to Vicious as an antagonist, so his past betrayal of Spike isn't surprising; its how far he took it.

Both met one another while working for a crime syndicate, but when Spike has an affair with Vicious' lover, Julia, Spike decides to get out and settle down.

This is when we learn where Vicious' loyalty really lies.

After possibly coercing Julia to sleep with him, he gives her the option of killing Spike.

Otherwise he'll have to kill both of them himself. 

3. Sōsuke Aizen (Bleach)

Sōsuke spent a lot of time developing an alternate persona that the members of Soul Society came to know and respect.

Merely a facade put in place to draw away attention from his plans, Aizen shocked everyone when he defected to become the acting god-king of Hueco Mundo and murders numerous people to keep his plot running smoothly.

It's a far cry from the bespectacled division captain the audience met initially. 

4. Villetta Nu (Code Geass)

After sustaining an injury, Brittanian Villetta develops a case of amnesia and is tended to by rebel Kaname Ohgi.

The two develop a rapport and, eventually, a romantic relationship. Villetta's usual sectarian ethics are even overcome by her new found love.

Then her memories return, she finds herself disgusted that she engaged herself with an Eleven, and shoots him. 

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5. Gendo Ikari (End of Evangelion)

After the death of his wife, the only thing Gendo is married to is his work.

Deeply entrenched in the politics of NERV and SEELE, it comes as huge shock when he blows off both of them in favor of creating the new human race with Rei.

Graphing Adam into his hand, Gendo puts the end of the world into motion.

It never occurs to him that Rei might decline the invite to be his "Eve," leaving him alone in his last moments. 

6. Kyubey (Madoka Magica)

The little mascot proves himself nefarious when he reveals the whole "magical girl system" is just a ruse to gather energy.

Rewatching the series makes every one of his cutesy moments more disturbing, whether he's rolling around on the ground like a cat or eagerly explaining how all the girls' problems could be solved if they'd just make that contract. 

7. Griffith (Berserk)

Griffith's vision and loyalty to his men are the glue holding The Band of the Hawk together, so it comes to a shock to everyone when he literally tears them apart.

Abandoning his comrades to become a demonic god, Griffith sacrifices them all to obtain his new abilities and powers, with only Guts able to escape in tact.

The rest of the story hinges on Guts' quest for revenge, and a solution to Casca's resulting instability. 

1. Anthy and Utena (Revolutionary Girl Utena)

Throughout the series, Anthy plays the victim to the abuses and manipulations of the Rose Bride system.

And maybe she is. The complex characters throughout Revolutionary Girl Utena leave plenty of room for analysis.

Shoehorned as a witch, devout to a brother she loves and simultaneously disgusts, and torn between a friend claiming to champion her freedom but betrayed her trust.

Finally Anthy chooses to do what she knows best: stabbing someone in the back. 

(source:animenewsnetwork)