Rerolling is a way to get the rarest characters in games which has gacha system. Players have to spend gems to roll a gacha, and characters are randomly distributed. Most of those games allow a player to roll a gacha without charge or by less cost at first time and that happens after tutorial. If players cannot get a best character at that time, they uninstall the app to try to roll the bonus gacha again.
The most efficient rerolling
Install the app.
Finish the tutorial 1.
Finish tutorial 2 and receive presents.
Finish tutorial about enhancing and awakening.
Play multiplay mode to get more than 30 Ninja Pearls.
Conduct Running Start Summon ( multi Gacha ) after obtaining enough gems.
If a character you want to get appears, finish rerolling. If not, uninstall the app and repeat from step 1.