Build wise, this is what I came up with. Click Slash!
Some explanation on the choices.
Gravity Break: It's a basic sub-weapon skill, but having good damage and a fast CD makes it great for spamming when other skills are on CD.
No Stronger Energy Barrage: Yeah it's neat and has KD, but the 20 sec CD kinda makes it limited. Also Concentrated Kamehameha, while having a longer CD, only needs 1 SP and comes sooner so...yeah.
Energy Barrage: What @opris35261991 said.
2 SP in Hit Rate Passive: Makes up for not using Roar. Not much of an issue since Swordsman has high hit rate to begin with, but it's still good to have.
Kaio-Ken: You're going to need its damage boost. It's that simple.
2 SP in Concentration: The skills with the longest CD are Concentrated Kame (22) and Burning Attack (20). Everything else is either 10 sec or 6 sec so fully investing in this buff felt unnecessary.
Everything else is standard for a Swordsman.