First Bite+Grants allies within 2 spaces Def/Res +2 through their next actions after any combat this unit initiates.
This family of weapons share a unique effect: They grant a defense and resistance bonus to allies. There are two different variants of this effect: Some grant a +4 bonus to adjacent allies, while others provide only a +2 bonus, but to allies within two spaces of the user. Compare to most buffs, these are offensively activated, triggering when the unit initiates combat. The nature of the buffs themselves are of the Hone/Fortify variety, appearing as blue on the character screen. The method of activation is somewhat less reliable that other buffing skills, but nonetheless it can provide a powerful boost to allies.
By nature of providing tangible buffs, these weapons have natural synergy with many things. First and foremost are powerful Blade tomes, who become stronger the more buffs are activated on the user. While they tend to prefer offensive buffs, defensive ones are still valuable, and can allow Desperation attackers to survive hits they otherwise could not. Being an offensively-oriented skill, they also have synergy with other skills that trigger from launching attacks. Death Blow, Armored Blow and its variants will all help the unit either KO their foe or take little counterattack damage.
The major weakness of these weapons is the activation requirement. Attacking is not always ideal, particularly if the foe has a special charged, or a Distant/Close Counter. Additionally, the unit wielding the weapon does not receive the buffs themselves, and must enter combat to grant them. In terms of weapons suitable for Player phase builds and units, there are much better choices. Brave weapons are arguably much more powerful, and can outright KO foes given the correct build. Finally, there are much more reliable choices for buffing allies. Special class teams have access to their unique class buffs, regular Hone/Fortify skills accomplish the same thing, and are easier to activate. Dual Rally skills also provide a large benefit, and they do not endanger the buffer.