aside from kanami. does any one know of any attack sealers?
Ninja's ranged attack "shuriken" has a chance to stun/interrupt, the character you mentioned is a ninja from SR and there are a few others available.
has any one found a reason to choose a duplicate of a card? if it's anything like gatcha's, dupes are always needed lol.
None that I know of, though the whole system has me largely confused at the moment, for example there are sets/pairs of cards that you can "complete" (Lia, Maris and Kanami is one such set for example) but I have no idea what that actually does.
There also seems to be a significant variance in card strength, which really annoys me since I have to fight a boss that randomly replaces people in your lineup and the entire fight is just RNG, and the fight itself takes forever, there seems to be no way to lock out certain cards so he'd switch in people who have no attacks left and that just screws you.
There's also variant cards, like different styles of Sill, and I'm not sure what the deal with that is beside them typically having other spells/elements.
Also, to add to your guide on the previous page; skills vary in whether they cool down or ramp up, there seems to be three categories and as a rule, charges/ramps reset on "resting" spots. The three categories seem to be:
Normal skills; these cost a set number of AP after which they cost one extra AP on the next turn, but never more than one (so using the same skill would be 1->2->2->2 and never 3 or more) however not using that skill on a turn resets it to the original costs.
Charges; Can only be used a certain number of times (generally just once) and need to be reset by resting to use again (Maria's fortification skill, and one of the Kalar ghosts' skills)
Ramp; These basically just cost one AP more each time you use them, this seems to include health recovery spells and some other effects (like Maria's Tulip) keep in mind not all support/recovery magic has this handicap. Church knights for example heal you on each attack and this doesn't ramp, and Kalar archers have a status recovery that doesn't ramp either (but also doesn't recover health)
Rance, at the end of Rance Quest Magnum.
Say any strategy or what must to do for save all country in 1st playtrough , seems impossible for me
It's probably possible, though if it is it probably requires a lot of know-how and luck on getting certain cards, same as how a no-casualty run is possible on the first playthrough of SR but you'd need to fight 4-5 different factions at once and engage at specific times etc. There certainly seem to be a lot of instances where there are alternate routes leading to/from fights that you're generally meant to lose (like Anise first time where you only get 4 turns before you flee)