general setup:
tick the following skills -
*Absolute Phenomenon
*Seventh Strategem: From Thin Air
*Sacred Cantata
*Skillful Means (on main DPS, LB0 Inori)
*Yo-arashi
*Full Enhancement (to force the game to swap Inori during turn 2)
*Dampening
(set up the chains of characters so that they have exactly the amount of SP to do their skills by turn 2 and 3, does not apply to Yunyun)
During turn 3: Inori has exactly 13 SP which is enough to do EX. At the same time, Wakkie has 9 SP exactly (by equipping a +2 SP chain she starts at 5SP - 7SP - 9SP) at turn 3 to perform DEF DOWN. Yunyun has non-zero SP so she can perform EX again.