Sera Beast

The strongest beast-summoner Reyvateil-type enemy, although she doesn't have any actual summoning skills. Despite this, she still remains an strong enemy not only due to her extremely high stats, but also because her Reverse Youth attack lowers all the parameters of the character who got hit with it, and additionally she can use a Lv. 3 Stored Attack called Poisson Cool, which deals large Thunder-elemental damage. Be careful with the massive debuffs she can cause, and hit her as fast and hard as you can.