So in this AU When Yuna was steeping in the bear gate a portal suddenly appeared which is connected to the void and a sudden force came this force is non other than a stray dense magicule wave that was sent from the cardinal world caused by the tenma war aka a miss fire when Rimuru and the others were fighting yuuki. This is when Yuna was departing from the capital, also the timelime in tensura was 50 years after tenma since the timeline was different but it synced after yuna crossed worlds..and why did yuna go to the cardinal world, simple the attack came from the cardinal world resulting in her being affected by the cardinal world and the voice of world sending her there. This story is inspired by @VOID-KING