Sparkle Arrow is a weapon for Shana/Miranda. It can be found in a chest on the ground floor of Indels Castle in Bale, near the stable area. It can also be bought in Bale's weapon shop for 50 gold. In battle, it will deal Light-based damage to enemies.
First, the good news. Shana with a Sparkle Arrow at 9 Attack is better armed than Dart with his Bastard Sword's 7 AT, from Bale until Kazas, at which point they will be even if she gets the trusty Long Bow (18) and he gets his Heat Blade (18).
Sadly, unlike the Heat Blade, the Elemental damage effect of the Sparkle Arrow is almost entirely useless to players seeking efficient play, as there is exactly one boss and one rare enemy vulnerable to it between Bale and Kazas. Players can take Shana back to Shrine of Shirley to find Dark Element enemies, but otherwise the Sparkle Arrow is useful only for its 9 Attack.