As the name Morrigna implies in mythology, war goddesses, you are likely to assume a Valkyries of Valhalla imagery. The Bua skill will boost up the charge rate of the affected character within a few turns. The drawback is the exchange of defense for dodge rate. Kind of like a berserker buff. Your affected character will go all out racking up the charge. At least there shouldn't be raised hostility? If the character can compensate the drawback with the charge attack, maybe, things will run smoothly. If not, well, at least the skill is a charge battery. Maybe familiarity with Narmaya will help out here.
The Glory for the Fallen support skill is a benefit at the cost of a fallen ally. If you happened to have any characters with revive skills around, consider Morrigna as some coverage of insurance when your party gets picked off one by one during a Impossible raid battle. Combined with Nier, Vira (Wind), or a switchable character as a sub ally, your revived ally will be back up within a few turns.