DFFOO [JP] Kain LD/FR+3/FLv.20, Launch + Counter + Off-turn Force Time HP bonus with Shadow
Very intricate and complex system, and it is REALLY hard to find a tanky boss that the team can manage the orb and have enough time to build force gauge with 2 non-force awakened characters before the boss dies, and ... the boss needs to be launchable and have a lot of turns.
So even though Leviathan resist critical hits, it would have to do for Shadow. I forgot to switch Ashe LDCA out for Cait Sith's such that Shadow can crit and have extra BRV, but this attempt is to show more about HP bonus stacking, less about dmg.
Force Gauge:
Force gauge appears if the game detects the presence of a force awakened character, be it your main party or a friend unit. It charges whenever a turn passes, enemy or friendlies, regardless of whether the character is force awakened. The charge speed can be increased by force awakening levels. At 100%, you can use force abilities to enter Force Time (FT), which grants an additional HP dmg bonus modifier for all members on top of existing summon blessing, BT effects, UW increases.
FT duration decreases whenever your turn passes. You can however build the HP dmg bonus in off/enemy turns if conditions are met WITHOUT depleting the timer.
Force Awakening:
At Lv 3s: +10% team-wide charge speed increase
At Lv 8s: +1% HP dmg bonus in force time when self turn passes
Note: this is only for self-turn and it does not stack when others have the same passive. So even with 2 awakened characters, you still get at most 3% out of this
Lv. 5, 10, 15, 20: S1, S2, LD, EX breaks BRV/ HP dmg limit when force gauge is above 80% (blue hue around the skill buttons)
The percentages differs from characters to characters.
Also the respective skill changes caused by these abilities tend to get the limit break as well. For Kain, his W Jump is tied to the LD.
Lv. 25, 30: Grants +5% HP dmg bonus in FT when S1, S2 are used
Others: Arbitrary stats and CP+30 (you don't really run out of CP as you move up the levels)
Currently it is unknown what kind of benefits is planned for non-attack moves.
FR weapons in common: (At least what needs to be the basic feature)
At base:
You get 1 use, 5 turns, initial 110% HP dmg bonus, burns all 100% Force gauge after using Force Time.
Character specific HP bonus conditions are included, albeit at a basic efficiency.
+1: Use +1, the move has increased BRV/HP dmg
+2: Initial HP bonus +10%, Force gauge consumption upon ending -20%
+3: Duration +5, also it becomes an equipable passive
Character specific HP bonus conditions (Force time effect) has increased efficiency
Specifically for Kain's FR, his condition is
+2 (5) HP%: when party uses a range type move and their turn pass and off-turn range type dmg happened
+2 (5) HP%: after party launches the enemy
Bracket indicates the efficiency of LB3
I would say for Kain specifically, the standardised structure for his Force Levels, especially beyond Lv.20 are designed for him to have his BT. If you think about how you can build HP dmg bonus with Kain and the condition associated with his FR, realistically you would opt for him to be the off-turn range dmg dealer by flying away and let other people take over. The other person can be a consistent launcher, a BT user with a Cid Raines CA and fulfil the other condition at the same time with Kain building HP bonus with Lancet.
Cross referencing his awakening levels, his Lv.25/30 grants HP bonus when he uses his S1, S2. IMO it does not make much sense to use his S1, S2 in FT, EXCEPT when he started a BT phase and you come immediately back down from W Jump since his "next" turn comes up instantly. In his BT phase you are bound to use his S1, S2. So that would be useful.
For LD only Kain specifically, he may have turn rate using S1/S2 but I would rather use Lancet and get bonus every turn.
If we look beyond present time, say we are looking at Vayne or Lightning who spams S1, S2 consistently with consecutive turns, then this passive would make your investment worth.
Why Shadow and Selphie?
Because you can get range counter, active turn range dmg with Shadow while Selphie make every active attack you do launches on top of Kain's own Lancet, satisfying all Kain's FR conditions in FT.
In addition, you can build HP dmg bonus in off-turns, specifically enemy turns with Shadow's counter and Kain's Lancet. Shadow's counter count as an off-turn dmg in this case. Since it is enemy turns, this part does not deplete FT duration whatsoever. Since Leviathan's veil delay your party by 2 turns every time you move, you build a lot of additional HP bonus just by letting them move and trigger the counters and Lancet. This is achievable with 2 non-Force awakened characters.
Tentatively I would say there is no need to invest all the way and you have to make character specific judgements on the worthiness of your investment, especially LBing FR and Force Levels. IMHO the speed bonus may be good pass Lv20, but the HP bonus is so negligible and the Lv.25/30s may not be worth for your character.