I've been pondering about this for a while so here I an sharing what I've been thinking about
"It just so happened that a crazed dragon drove a hole into the dimension wall , creating a passage for souls to be randomly transported across worlds"
Could it be that Yanu was the who tore the hole in the dimension wall in search of his mate? Because remember that Eyra is not the only transmigrant / isekaid in their current world.
can anybody spoil me what will happen next