If you prefer to modify your own progress rather than downloading someone else's file, save editing is a highly customizable alternative. Using CWCheats (PPSSPP)
No, not officially. The Achilles and Epsilon units are unique bonuses specifically locked behind having clear save data from the first game and BOOST respectively. danball senki w save data
With the PlayStation Store for PSP/Vita sunsetting new purchases (and the servers for Danball Senki W officially dark), your save file is the only museum left. If you prefer to modify your own progress