|This build allows Felicia to be both incredibly offensive and supportive specializing in utterly crippling a single threatening unit while providing a slight debuff to surrounding units while at the same time healing ally units. There are two weapon paths one can take depending on whether they want our lovely Felicia to be more offensive or defensive. (I find that this build truly shines if there is a dancer/singer unit on Felicia's team.)
Felicia's Plate - Hits the lower of the foes Def or Res making her damage more reliable. In addition to her double Poison Strike dealing 20 damage after combat, this weapon allows Felicia to leave any opponent weak and vulnerable to be picked off by ally units. Additionally, it inflicts -7 Def/Res on units within 2 spaces of the target.
Dancer’s Fan+ - Damage output is weak on foes with high Def. The primary difference is with this weapon Felicia is able to heal adjacent allies for a total of 14 hit points after combat but only able to weaken 1 unit.
Refinement - I chose the Res refinement because it both enhances Felicia's ability to tank mages and it further boosts damage from Glacies. However, you can do what you want here.
Reciprocal Aid - Allows Felicia to essentially self-heal. If she takes damage she can swap HP with a healthy ally and then heal them for +7 HP or +14 depending on her weapon.
Glacies - Need I explain why were are putting this special on her?
Resistance 3 - Boosts damage from Glacies trigger in addition to being a reliable form Res when Felicia is both attacking and being attacked.
Side note - if you want more powerful mass debuffs I would advise using both the Savage Blow seal and skill. However, you would have to sacrifice the heal from Breath of Life.