My-Otome Zwei
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.
Read more about this topic: Erstin Ho