The protagonist Stan traveled to the world of Zeta, and after meeting Zero in the Kingdom of Light, he successfully became Zero's apprentice, and he was still before Zeta
Sero: Zeta, you really don't let me worry! Learn from Stan
Zeta: It feels really bad to be compared to me by my master.
Stan: I will be optimistic about Junior Brother Zeta!
Intention: Justice will prevail