DWS
Writing
of reading
154
Read books
The gun (more specifically the cards) target people who have an interest in the MC, mostly as they are familiar with a fictionalized version of them from their own universe. It's not brainwashing - they're simply taking people from the infinite multiverse who already feel that way and are willing to help fight.
( ͡° ͜ʖ ͡°)
That's a little out of the scope of what I've written (so far,) but Mitsuru never says no to an ambitious idea - with enough mastery of the technology it's entirely possible he could in the future.