The Illumina is the most powerful sword in SFOTH strength-wise, doing 40 damage for a lunge attack. It's lunge makes you jump higher than other swords, and it's sparkles reveal any invisible opponents. It's only real cons are that it's sparkles reveals your location, and lunging leaves you vunerable for longer.
The Illumina is a LimitedU gear. There are only 100 and the cheapest price people sell it for is a gob-smacking 1,000,000 R$.