Erstin Ho (エルスティン・ホー Erusutin Hō?) is a fictional character in the anime and manga My-Otome. She is voiced by Minami Kuribayashi in Japanese and by Lori Barnes-Smith in the English version. 
She is one of Arika's roommates and a good friend of Nina Wáng, as well as being the 17th Coral in her class. She is sweet, friendly, and often quiet. Hailing from the country of Annan, her parents are wealthy enough to pay her hefty tuition fees. She and Irina serve as Akane's room attendants.
Erstin harbors romantic feelings for Nina, which was most evident in episode 6. During a pool scene, a creature was swimming around tickling the girls. Erstin thought it was Nina who was behind her and told her that if it's her, she's fine with it. When Nina nearly drowns, Erstin performed CPR on her in a rather affectionate way.
Erstin quickly acquainted herself with Arika Yumemiya and didn't hesitate to help her in the best ways possible. She comforted Arika who at the time was being plagued by thoughts about her love towards Sergay. Erstin herself knew she wasn't as strong as Nina or Arika, so she did her best to support them in the best ways possible.
During episode 16, Erstin found out that Tomoe Marguerite was responsible for the many strange accidents that Arika was suffering from. When Tomoe was about to drop acid on her, Erstin shoved Arika out of the way and took the shot and fortunately suffered minor injuries. Strangely, she did not speak out.
When Schwarz launches an attack on Windbloom, Erstin is revealed to be a spy and agent of Schwarz and uses a sickle wielding Slave. Smith, a Schwarz agent, orders her to kill Arika, but she hesitates because of their friendship. Unfortunately, she is killed when Nina (who had just activated her Meister Robe) tries to attack Arika. She commands her Slave to block the assault and as a result, it is destroyed by Nina's attack, ending her life. While Arika was reluctant to fight Nina before, Erstin's death serves as a trigger that changes Arika's view and results in the beginning of a rivalry between the two girls.
It was revealed that the Ho family provided many Otomes to Garderobe who unfortunately fought in the Dragon King War, suffering in many casualties. This prompted the family to join Schwarz and support them in which Erstin was forced into the cult.
Mashiro mentioned Erstin to Mai Tokiha due to the issue on the SLAVES, saying it was pitiful for Erstin to carry a SLAVE. In the preview for episode 4 of Zwei as the characters are saying what they wish for in the next episode, the voice of Minami Kuribayashi (who plays Ribbon-chan) is heard switching to her Erstin voice and saying that she hopes to stay alive until the end, after which the other characters are heard laughing nervously.
In the fourth episode when Yuna is attacking the Black Valley Ribbon-chan tells Nina that she will use her SLAVE to fight and protect people, at which point Nina has a flashback to Erstin and finds the will to fight alongside Arika and Mashiro. At the end of episode 4 Ribbon-chan is seen walking up the stairs to Garderobe and declaring that she will become an Otome, and at this point the audience can see that under her hood she bears a remarkable resemblance to Erstin.
In the manga's universe, Erstin's character is largely the same, including her crush on Nina and later Manshiro (a male body double of the real Mashiro) believing him to be a girl. But she is Coral No. 3 in the manga. This version of her character is noted as having F-cup breasts by Arika, and appears to suffer from androphobia, or fear of men. This was due to men drawing undue attraction to her larger-than-normal bust. Her oneesama is Shiho instead of Akane as in the anime.
She initially hated Arika for separating her from Nina because she had to move to another room to make space for Manshiro, which made her an easy victim for Shiho to manipulate into fighting for the Blue Sky Sapphire. She was the second of the initially-ignorant to discover Manshiro's manhood, when she was an accidental witness to him urinating, a discovery that horrified her. However, after Manshiro protected her during a Schwarz attack, she managed to accept the truth. She refers to his penis as an "elephant". Eventually, she "persuades" Natsuki to let her move back into the room occupied by Arika, Manshiro and Nina.
Unlike the anime, she is not a member of Schwarz. Although she comes close to death as a result of a self-directed suicide bombing aimed at Duran, she never actually dies. Eventually she gains a Meister Robe, the Rainbow Cloud Rhodonite ( 綵雲の薔薇輝石 Saiun no Barakiseki), of her own and is vital in defeating Fumi and the revived HiMEs.
- Erstin's name can be romanized as "Elstin Ho", an anagram of "Holstein", making her name a pun of her large breast size. This is played upon in the My-Otome Arashi spin-off manga, when, after being caught trying to seduce Arashi to free Mashiro she is dressed up in a cow costume and shipped off to a farm as punishment.
- Erstin's large breast size and frequent mention of it is likely a reference to Mai Tokiha, the lead character of My-HiME, whose bust was also a recurring subject of discussion in a humorous light. This is even more evident in the DVD special Juliet's Conspiracy where Nina bumps into her breasts just as Mikoto used to do to Mai.
- My-Otome DVD Ending Credits