Wain, Sven, Marlis, and Osvald were watching Nitra and Liang's fight just like Alucard, but he, unlike them was not a ghost who watched memories. This Alucard was real and could change the outcome of the fight if he wanted to.
Nitra recovered, and Liang gradually became stronger and stronger enjoying the fight. The stronger the opponent was, the better it was for him. So, if Alucard stopped being a spectator, things would immediately change.
He could help Nitra, in which case Liang, The Strongest One would lose which would be an event of historic proportions. Or he could kill Nitra and together with Liang destroy the Tree, it would be a real disaster and tragedy for Constructs for hundreds of years.
It was unknown how long it took for a new Tree to grow and whether it was even possible again. A third Tree might appear, or perhaps the current one was the last and its loss would mean the end for an entire race.
