These three warriors are not currently immortal, but Bon recognizes their potential to aid Fushi and wants him to develop a "reserve" of personas in case the Nokkers steal his existing ones.
Strengthening Prince Bon's character from an "obnoxious" figure to a pragmatic and surprisingly strong leader.
Because Bon knows Fushi has the power to bring people back to life (a fact Fushi still doesn't realize), he starts making his own secret plans to leverage this ability during the upcoming war. Viewer Perspectives
Fumetsu no Anata e Season 2 - Episode 11 discussion : r/anime
