Super late, but...

I've been playing since elementary school, so if you only count my Nyan-ko history, it's been 5-6 years, and I've finally reached Angel Cannon level 30. I've progressed to Zero Legends, but I haven't properly upgraded anything other than the Cannon Turret and Angel Cannon. There are too many 'stop invalid' enemies, so maybe Cannon Break Cannon or Iron Wall Cannon will be stable next?