World 5 is day maps so bulking up tachi and ootachi will work. World 6 you want to take a party of tantou and waki with a token uchi for waki-uchi combos (and the final boss).
Night time = small light swords.
Day time = big fat swords.
Open field = long range swords and whatever projectiles you like.
Houses and side streets = one target only, no horses, consider: guns.
You will lose troops and suffer damage from yari in world 6, it is guaranteed, but until you have kiwame just keep going until someone hits red. You never know when you might luck out and everyone leaves alive in orange with no troops left.