User blog comment:Mich, Michele & Kuhla/Guide: Achievement System/@comment-146.186.57.83-20150916192608/@comment-26344181-20150916212745

Do a quest that has lots of rounds, Maybe 12+. Or do one with a high-HP boss.

Use HC buffer units - Diana's BB, Aurelia's LS, Luka's LS is EXCELLENT for generating HC, etc.

Use their BB/LS and attack each unit individually (tap them to target them), and use units with high hit counts (Len, Bestie, etc.). That'll maximixe HC drops.

That's all I can think of though, so good luck!