I could have made this an Enchant Player Aura, but it seems more interesting this way, being flavoured as a sword that the player can actually hold.

Additional Rules:
Wielding is analogous to equipping, but for players instead of creatures. Armament is Equipment for players.
If a player has any power, he or she may choose to deal that much damage, divided among a number of unblocked creatures when combat damage would normally be dealt. Rules for dividing combat damage between multiple targets remains the same as for creatures. Damage dealt by players this way is normally considered to be combat damage from a colorless Planeswalker source. Players' colours, types, and stats can be modified.