Attack on Titan may have ended, but its story and legacy won't be forgotten anytime soon in the anime/manga world. Although creator Hajime Isayama has been adamant that he has no plans to create a sequel series, that hasn't stopped fans from finding new ways to see their favorite characters again.
For example, the case of a cosplay enthusiast below took advantage of his forte, to revive one of the important characters in the series through cosplay. This person transformed into Ymir, bringing back the first Founding Titan, after playing an important role in the Attack on Titan series.
As fans know, Ymir was instrumental in giving Eren Jaeger the power of the Founding Titan. Unlike many before him, Eren was able to strike a deal with Ymir and the Founding Titan granted the young man his full power.
Eren used this power to unleash the Tremor, along with creating a new form for himself as a giant skeleton. Defeating Eren seemed impossible, but was eventually achieved by Armin, Mikasa, Levi, and the Scouts.
One of the biggest plot twists at the end of the series is that both Ymir and Eren see the future and see the Quake as the only way to ensure a future for Eren's friends. This plan finally gives Ymir the peace she has been searching for for hundreds of years as her love for someone who is not worthy of her, leaving her trapped in her duty as the Founding Titan forever.