Hero class: Melee tank.
The best early game tank and one of the best tanks mid-game. Arguably the best tank overall due to the first skill which greatly reduces damage taken from melee enemies.
Use cases: Her usage is rather simple: while standing in the middle of the first row she concentrates enemy fire upon herself. She has one of the best starting blocking bonuses, so she has a certain advantage over other tanks which makes her a really tough tank to beat down.
Equipment: She undoubtedly needs a tanky equipment set.
Synergies: It’s quite enough to have one tank, so the rest of the heroes in the rally with Giranna are best to be damage dealers or support heroes. She obviously has great synergy with Dwoggour, and also with Aatu, who can debuff enemy ranged units while Giranna does great against melee ones.
Units: Since she is to be a frontline tank, she needs the tankiest units, especially considering that she doesn’t provide any DPS buffs to allies. Most likely the choice will be lying between usual shieldmen and those with a good mag defense, depending on the rally setup. However, the usual shieldmen are more universal and tougher in most cases.