Seifer is a denizen of Twilight Town that appears in Kingdom Hearts II, and is based on the Final Fantasy VIII character of the same name. He is the leader of the "Twilight Town Disciplinary Committee", and an avid Struggle player who won the championship in the real Twilight Town, in place of Roxas's victory in the digital version. Seifer is fought only in Struggle battles; on the first day, Roxas fights him at the Sandlot in a combat tutorial, and during the Struggle Tournament on the fourth day, he can find Seifer again at the Back Alley after defeating Hayner.
Seifer's normal stance is guarded, so if Roxas/Sora hits him the attack will be deflected. However, he is easy to defeat as he has lower health than Hayner or Setzer. Seifer's main attacks are a basic slash and spin attack. Both are easy to parry, so attack when the possible. Roxas/Sora should easily be able to deflect his attacks and return with a combo.
After several combos, he is likely to jump high into the air, saying "Isn't this romantic?". He will then come down with his blade outward. The best way to avoid this is to run toward him or to run sideways, as the attack has limited range. One can also simply walk behind him as he descends, so his attack passes right over Roxas/Sora without danger of being hit. Avoid jumping while Seifer is performing this move, because he will hit Roxas/Sora and send him flying regardless of whether he is parrying or not. The only way to recover from this is by using the Aerial Recovery technique.
When playing as Sora, if doing a rapid attack (due to something like a Berserk Charge), Seifer will block the next attack, spin toward Sora and attack. Beware of this and make sure the finishing combo is usable. Another way to easily win is to use Trinity Limit. This will almost completely remove all of Seifer's orbs; simply collect the orbs and the battle will end.