Magical Girl's Knight Brother

Due to an accident, Tang Zijun traveled to a parallel world.
Along with him, there was also an unknown Kamen Rider belt.
After discovering that a strange underworld, the Mirror Dimension, was hidden beneath this world, Tang Zijun, all alone, spent several years successfully wiping out all the monsters in the Mirror Dimension.
At the same time, he is gradually adapting to his new identity.
Just as he was living a peaceful life as he had always wanted, Tang Zijun accidentally discovered her sister's secret—she was actually a magical girl!
Could there be factions in this world that even he doesn't know about?
Is the Mirror Dimension the only evil monster?
Was he really going to just stand by and watch his sister live the same precarious life he had once lived?
In this regard.
Kamen Rider Tang Zijun, who had been retired for seven years, reluctantly picked up his belt again.
"Don't blame me, blame yourselves for messing with the wrong people."
"henshin!!"
...