The Javelin (also called the Spear) is an essential tool acquired towards the end of Phoenotopia and Phoenotopia Awakening. Gale obtains it from some rescued Daea soldiers after dispersing the Daea Guard Horde. As its name implies, the Javelin is a wooden spear that can be thrown like a projectile. Although it can damage enemies, the Javelin's primary purpose is to help with platforming, as it will stick to any wall it hits and can be used as an artificial platform, making it easier to reach areas Gale wouldn't be able to get to on her own. Many parts of the Prince Tower require the Javelin to navigate, and several areas afterwards (along with some secret areas) also make it necessary to use.
It is possible to enhance the Javelin's power by obtaining the Ki Spear Technique Scroll from Aella as a reward for restoring her memory. Said scroll enables Gale to charge the Javelin so that it can be detonated at any time after it's been thrown. This ability makes the Javelin very useful against some types of enemies and able to destroy some barriers the same way Bombs can.
The Javelin is also the Kobold General's weakness, as it's the only weapon that can pierce through his defenses, and even then it only hurts him when he lowers his force field to charge up his special attack.