Honestly, I really really like the mechanic of building up the attack through multiple presses, it really changes up the gameplay of this style, where you can't just constantly rain attacks onto the boss, that's a nice concept.
The dodge ability probably needs a cooldown, since right now the dominant strategy is just to spam dodge and charge at the same time until you hit 6 charges, then just dodge until you get underneath the boss.
Some animation for the boss to spice him up would be a welcome addition. Also moving the charge indicator near the player so they don't have to switch focus between the top right and their character so often would be a nice touch as well.
Overall, really fun boss fight! Great work!