>>712781395
Congrats! Looks like it finally clicked for you. And while you do not need anymore help with the fight, I did notice somethings that will probably help you with future fights.
1. Stop using Slash in boss fights. That's an Area of Effect attack and is best used against mobs of smaller enemies. For boss fights, instead use Shield Break (to break enemy shields), Shock Wave for a ranged attack, and Triplet with is the best single-target Beta Skill. In particular, Triplet becomes very useful as you can take off a single unit of an enemy's Balance (Yellow Diamond) as you upgrade the skill.
2. When the enemy glows Red, lean into its attacks. The Red glow means the enemy is about to swing at you a bunch of times, which means you can parry them a bunch of times, which means you can deplete their Balance faster. The Red glow is an opportunity and you want to take it.
Outside of that, you look like you're doing great