"This is a simple, clean-ish (I made some blunders since I was trying to make it quick) Massive Victory for Free Battle No. 026 Colosseum (Megumi's Counterattack) for the Meat Grinder achievement on Steam.

Note how I took advantage of the "Cat Ears" (you might have to beat the second Cats battle for this?) and "Curry" modules to make Heshiko the equivalent of Mr. Cat and ended up keeping a spare Himiko at the rear in case I lost the Heshiko Command Tank in battle. Also note the variety of units I utilized (although I actually didn't use shock tanks Gonta's can be really useful with a daisy bomb and move+# modules) to secure the victory.

Main points to winning the Megumin Free Battles:
+ Be aggressive with Mr. Cat and Heshiko.
+ Take advantage of KRR Rara with Target Area + 2 and maybe a Range + or Cola/Curry/etc. module.
+ Keep fast Line-Mon in case lone enemy units make it to your back
+ Try to get rid of the Cats and huge Laser Tanks early as they'd be the most likely to wipe you out."