if im not mistaken, how much initiative different in term of value also play important role.. but the difference must be a lot..

for example in your own lineup, if your P2 have 10k initiative more than your P1, P2 will attack first.. then your P1

i've tested in 9 tail invasion where i'm using sasuke normal BT as P1 (i want the lightning barrier) & LM as P2 (main damager)

since my main have highest BP as well as the initiative difference value is more than 10k between LM & sasuke.. so in that situation, my LM will attack first prior sasuke even though sasuke is P1

in order to make sasuke act first for me to do mystery lightning barrier, i removed all initiatiave runes from my LM & it works

when fighting opponent.. standard action turn who will attack first is P1, opponent P1, P2, opponent P2.. and so on..

in P1, who will attack first depends on who have higher initiative (if opponent P1 have higher initiative than your P1, your opponent will attack first)

and so on so forth for P2, P3, P4 (if opponent P2 have higher initiative than your P2, your opponent will attack first)

however, if your opponent P2 have more than 10k initiative than your P1.. the order of action will be opponent P1, opponent P2, then your P1..

u can test it by fighting your server highest rank player

good luck