JMS v302 - Kanna

Since I became Kanna120Lv, I tried to solve your question.
Booster doesn't not influential to Haja Rengekihu. Maybe that is fixed to 330ms.
Shisen Gyouha activate Shoujou Kasyu. I confirmed it.


Haja Rengekihu is better than Shisen Gyouha.
In JMS, we greatly care about "the number of hits per minute." Because we consider the case that we reached to 999,999 damage.
In a minute, Shisen Gyouha(270ms) hits: 222 *2 +222 *0.6 *3 (Shoujou Kasyu) = 621 times
But Haja Rengekihu(330ms) hits : 181 *3 +181 *0.6 *3 = 868 times

And Shisen Gyouha doesn't put into motion "Boss damage +%" like DemonSlayer's Demon Slash.

But when you use 孔雀開き, 紫扇仰波 = 240ms, Hits: 250 * 2 + 250 * 0.6 * 3 = 950
With a Viper, 210ms, Hits: 285 * 2 + 285 * 0.6 * 3 = 1085

Boss damage+% is certainly less effective, but it still works.
紫扇仰波 Damage = (100) * (210% + Boss Damage% + Total Damage%)

So if you can hit 999999 with 紫扇仰波 or have have less than 20% Boss Damage/Total Damage (AFTER SKILLS), it's better than 破邪連撃符.