What is a Blade Combo finisher?

Solution 1:

The Blade Combo finisher is the last Special Art performed in a Blade/Elemental Combo.

There are two types of combos in Xenoblade Chronicles 2: Driver and Blade combos. Driver combos are performed using Driver Arts and require using Arts that inflict Break -> Topple -> Launch -> Smash statuses in that order. Blade combos are performed using Special Arts (moves initiated with the A button). You may also know them as “Elemental Combos”.