After Ymir revealed that she is a Titan Shifter in episode 4, the mysteries regarding her true nature are expected to be unveiled on the next episode of "Attack on Titan" season 2.

In the previous episode, Ymir made a drastic decision to unbridle her Titan power to save the lives of her fellow trainees from the attacks at the Utgard Castle until the Scouts arrived from Ehrmich District.

But the trailer for the upcoming episode called "Historia" reveals there are more to Ymir's story that should unfold.

Based on the trailer, the Titan form of Ymir will be facing several Titans in battle, while her fellow trainees watch on top of the Utgard Castle. It also shows several scenes where Ymir and Christa are training on top of a snowy mountain in the past, where Ymir reminded Christa that she should live a life that she can be proud of.

However, the trailer does not reveal the reason why Ymir wants Christa to remember that promise. Moreover, the clip also shows that Christa will worry about the welfare of her friend, while she is being attacked by the other Titans. In the sneak peek, Christa is seen screaming for the life of Ymir, while casting aside her hidden personality.

Ymir's and Christa's stories are expected to be revealed in the second season of "Attack on Titan" based on an interview with director Tetsuro Araki by ANIPLUS Asia.

"Character-wise, we have some that never really got the spotlight like Ymir or Krista, and we get a closer look into them now," he said. "That's going to be a big highlight, I think," the season 2 general director stated. "We discussed the dramatic points of those parts a lot with Isayama-san and managed to delve even deeper into them. We hope you look forward to it."

The upcoming episode of "Attack on Titan" season 2 will be released in Japan on Saturday, April 29, but it will be streamed online through various websites such as FUNimation, Crunchyroll, Hulu, and Anime Lab.