You can zip through some obstacles with U+D / L+R inputs.
When Kazemaru joins, his level will be (the main hero's level) - 1.
So, if the main hero's internal level is 0, Kazemaru's internal level will be 255.
But anyway, you have to win the 1on1 battle against the last boss, and it will take a long time to earn levels.
I hope there are some more glitches to solve this problem.