Yandere characters in anime often do terrible things for the people they love or are obsessed with. Their heinous actions often included kidnapping the target of their affections, threatening/killing anyone else that came too close to their beloved, or a combination of both.
However, some yandere characters were more successful in achieving their goals than others, since they had more overall strength and wit to do so. They constantly schemed, threatened or eliminated any competition. They may have taken advantage of the protagonist to get closer to them. Likely, they would do everything possible to keep their loved ones away from anyone else.
10 Freya Was Obsessed With Bell And Tried Killing Hestia (Is It Wrong To Try To Pick Up Girls In A Dungeon!?)
Freya was deeply obsessed with Bell Cranel. This obsession led to Freya trying to get Hestia, the leader of Bell's Familia, killed during a festival. Freya deliberately unleashed several beasts from the Ganesha Familia's arena to terrorize everyone and destroy property. During this chaos, she had one of the strongest monsters chase Hestia.
This forced Bell to protect her, which foiled Freya's plans. Freya hadn't yet attempted to take Bell for herself. However, she took all opportunities to thwart others' attempts, such as killing Ishtar (who tried claiming Bell for herself) during the second season.
9 Haruna Niekawa Believed She Was In Love With Nasujima (Durarara!!)
Haruna Niekawa fell in "love" with her teacher, Nasujima, while under the demon blade's influence. Nasujima used his relationship with Haruna to extort money from her. However, Haruna believed that she was actually in love with him. The demon blade's influence grew so strong, she nearly killed Nasujima, despite her affections for him.
She also attempted to kill Anri after she realized that Nasujima started making advances towards Anri. Thankfully for Anri, Haruna failed to kill her.
8 Anna Nishikinomiya Threatened Her Rivals With Scissors (Shimoneta)
Anna Nishikinomiya is one of the main characters featured in Shimoneta. She seemed like the responsible student president. But, after she had her first kiss with Tanukichi Okuma, she grew increasingly obsessed with him.
She started attempting to get his "love nectar" and justified her actions as love-driven. She also thought of love as an act of justice to justify her actions further. Anna later threatened Ayame by putting scissors to her throat, after noticing that Tanukichi was getting closer to her.
7 Megumi Shimizu Truly Cared For Natsuno And No One Else (Shiki)
Megumi Shimizu cared for Natsuno Yuuki and no one else. After she became one of the undead Shiki, she started stalking him through the window. She killed anyone who would get too close to Natsuno. However, her attempts to be with Natsuno ended poorly, and she was eventually killed by the other villagers.
Her death differs depending on the adaptation. Shiki saw her hit by a tractor while being chased through a rice field, just before the rest of the villagers caught up to her and stabbed her with stakes through her heart.
6 Akane Hiyama Stabbed Anyone That Got Too Close To Seiji (Renai Boukun)
Akane Hiyama initially seemed very sweet and kind. Akane either threatened to stab, or actually stabbed, anyone that got too close to her classmate, Seiji. Akane believed that she was the only one allowed to harm him or be close to him, so she attacked anyone who attempted dating Seiji.
Akane became bound to Seiji through the Kiss Note. Unfortunately for Akane, the Kiss Note also bonded her to the cupid Guri and Akane's half-sister, Yuzu. This meant that Akane ended up with Seiji, but also she must compete with two other people over Seiji's affections for eternity.
5 Yamai Kidnapped Tadano And Threatened Him And His Friends With Chopsticks (Komi Can't Communicate)
Yamai Ren being a yandere was mostly played for laughs. However, her first appearance in Komi Can't Communicate's anime adaptation was no laughing matter. She kidnapped Tadano and held him as a hostage in her home in her debut episode, so she could have Komi to herself.
Thankfully for Tadano, Najimi grew suspicious of Yamai. Najimi deliberately asked to come over to Yamai's house with Komi. Najimi and Komi's impromptu visit ruined Yamai's plans to kill Tadano. Komi also told Yamai that she would choose her friends. This stopped Yamai from getting too close to her, and also saved Tadano.
4 Esdeath Grew Deeply Obsessed With Tatsumi (Akame Ga Kill)
Esdeath was a high-ranking general of the Empire, but she fell in love with Tatsumi despite him being part of Night Raid. She instantly fell in love with him after seeing his battle skills and his warm smile. Tatsumi tried to have her defect to Night Raid by exploiting her affections. His efforts were unsuccessful. Despite this, she would not let anyone else touch him, even after Tatsumi was captured multiple times by other members of the Empire. Unfortunately for Esdeath, her increased attention towards Tatsumi led to her demise in battle.
3 Toma Tricked The Heroine Into Believing She Was His Girlfriend (Amnesia)
Toma tricked Amnesia's nameless heroine into believing that she was his girlfriend. He initially appeared to be a kind boyfriend looking out for the heroine, and accompanies her on her outings. In reality, he was so obsessed that he hurt others that got too close to her.
Toma also drugged her food and later trapped her in a cage, to keep her from escaping him. Toma failed to take the heroine for himself in Amnesia, but succeeded in his visual novel's route.
2 Satou Matsuzaka Kept Shio All To Herself (Happy Sugar Life)
Satou was the main heroine of Happy Sugar Life and began living with Shio Kōbe after falling in love with her. Despite her cheerful appearance and public popularity, Satou was secretly obsessed with Shio. She lied about who she was living with, just so she could keep Shio away from everyone else.
Satou protected Shio, killing people and risking her life for her. The latter habit, however, led to Satou's demise since she died protecting Shio from a dangerous fall.
1 Yuno Gasai Protected Yuki No Matter What, Including Killing For Him (Future Diary)
Yuno Gasai was supposed to fulfill the Yukiteru Diary, also known as the Diary of Future Love, so she served as Yukiteru's main love interest. Yuno harmed anyone she thought would be in the way - including friends, rivals, other love interests, or family members. Yukiteru's promised to marry Yuno someday when they were young only strengthened Yuno's obsession with him. Yuno successfully ended up with Yukiteru at the end, living together through four different timelines.