According to Lucian’s lore changes, Senna’s soul was captured by Thresh, but Lucian managed to free her from it. The story refers to the new Lucian teaser: “Lucian … frees Senna but instead of her passing on like he intended, Senna came back corrupted, but in control of it,” according to a translation.
On the English website, Lucian’s biography ends with: “To Lucian’s horror, the creature tricked Senna and ensnared her soul, trapping her in a spectral prison. Nothing could bring her back. Senna was lost, and for the first time, Lucian faced his mission alone.“
This hint contributes to what we know about League’s next champion. This all began with a mysterious fog appearing in the Summoner’s Rift spawn. Then, more signs pointed at Senna as the next-released champion.
Senna’s survival is obviously mandatory for her release into the game. Since this change is live on China’s official website, it’s even more certain that she is the upcoming champion on League of Legends.