Long sword, as you should know, i WAS a longsword fanatic, but just recently i started useing hammers, BUT the one thing i still use longswords for is Kusharu. Devil slicer decimates lvl 4 kusharu. I would not recomend useing SnS on him cuz its got too short range. To get an idea of how the battle should go, here is my example:
1. use psn knives
2. Beat the crap out of it, till it falls over
3. Continue beating the crap out of it as the wind shield should be down from falling over
4. IF the wind shield comes back, flash it and beat it to make the shield dissapear again.
5. Cut off the tail once its health has gone below 40% of its total health and break horn.
6. Now its shield should be gone permanantly, now you win.
U know Ur am doing good if the shield never regenerates after you poison it, which means your damageing it soo much, that it falls over B4 its shield comes back.
Tell me if this confuses you.