A so-called "Secret Weapon" of the Harbingers
Bane is... well... let's be honest, he has a practically nonexistent personality. This is no fault of his own, but he is easily one of the stiffest people one will ever meet, often responding to regular humor and a number of human natures with a blank stare of "I don't get it." His mind is really only on the mission and how he can best accomplish said mission. Because of this, he's not exactly fun to be around, but he can, with enough insistence, be talked into trying fun things, though good luck trying to explain the "tactical importance" of bowling or playing cards.
Bane is quite possibly a living testament of rigorous training. He has mastered, or very nearly mastered, several martial arts and forms of combat. His favorites martial forms seem to be those related to eastern Wushu (Kung Fu) and Jiujitsu.
Physically, Bane's only weapon is a seemingly unbreakable (at least it hasn't ever been broken yet) bo staff made of some kind of metal. Interestingly, it's not actually a staff but in fact houses a trio of hidden spear blades (which gives the spear a cross shape) that can be switched out or retracted through some kind of mechanism.
Though Bane only carries his staff/spear on hand at all times, he is by no means helpless without it. If he doesn't use his bear hands or feet as lethal weapons, then virtually any object can be picked up and turned into a weapon of some kind.
Bane, unlike any other Slayer, wasn't raised with any semblance of a normal life. His Watcher was only interested in one thing: to turn the Slayer he was given charge of into a walking killing machine, and they did so. Bane's life was almost nothing but training, training, training, and more training. When he wasn't getting martial arts forms drilled into him, he was being hammered with all the various methods of killing vampires and lycans and how to best use those methods in a tactical sense. There was never any real childhood. No fun, no games, no friends, unless the practice dummies could be counted as friends, and certainly no love or compassion. As such, Bane grew up to be pretty emotionally stunted, not ever being shown anything like fun or other such human activities.
The other thing about Bane is that his existence was largely kept a secret. In fact, only Bane's Watcher knew of the training regiments. If other Watchers learned of such methods of raising a Slayer, then it would raise numerous moral and ethical debates and some might have even been outright furious at the notion of raising a Slayer like some kind of living weapon. And so Bane's existence was kept strictly secret until it was too late. Naturally, it raised all kinds of questions concerning the moral or ethical implications of such a project, but the damage had already been done. The Harbingers essentially had a super soldier on their hands, and they decided it would be a waste not to put Bane to use.