Speaking of Sephiroth.. I'm bored to I'm going to write a quick guide. (I doubt you may need it though =/ I dont care I'm bored)
--------------------------------------------------------------------------
he is so fun too beat up! it toke me 4-5 trys to beat him.. which is sad because he's not as hard as some people think, but I must admit even though he's easy to me, it does take a good amount of time to defeat him. In this battle against Sephiroth the 4 very important things that really helped were...
1.Dodge Roll
2.Equipment that raises HP,MP,DEF,STR but there not all required.
3.Strike Raid.
4.And focus
Once you get used to his movements he's no challenge, though u must be careful of his Sin Harvest... (Second Chance helps a lot!) it reduces all your HP unless u have second chance.., and takes down your MP to 0... Meh but u guys know about Sin Harvest. ^_^
anyways...
Level doesent do crap in this battle.. seriously..(and no I'm not saying enter the battle with a very low lvl) it depends on how much Health/MP/Defense you have.. lvl rarley gives you MP for one thing.. and that's really needed if your going to use attacks such as Sonic Blade, Strike Raid..To break through his magic armour... (using Sonic Blade isent so good... he teleports all over the place.. and you have to get close to him to use it.., but with Strike Raid u can attack him from far away, and he doesent do a teleport slash. (until he gets in your face, or after a few steps.)Make sure u use Lionheart for critical hits.. or w/e weapon you find helpful. If you have a good amount of HP/Def dont be afraid to let him smack you around a bit.. this will give u MP to get ready to heal, and enough to use another magic spell. (always keep pressing the lock button, that way if he teleports you can go after him with dodge roll and hit him before he uses Sin Harvest) I'm sure there are many other ways to take him down with ease though.
This is the method I used..
~Blade~