This is the boss guarding the Hymn Crystal Linker, and is accompanied by a trio of Wyrms. It basically is a pastiche of Dragon-type enemies you'll be meeting later on in the game, as it has several abilities taken from various of the strongest dragons. Its attacks are Dragon Kamikaze, which has a high critical hit rate; Poison Mist, which can Poison all party members; Fire Breath, which causes Fire-elemental damage to all party members; and finally, the Lv. 1 Stored Attack Assault Storm.
But objectively speaking, this monster is quite weak in comparison to previous bosses, especially the ELMA-DS you had to defeat to clear Phase 1, so it shouldn't be much trouble to defeat it; and in fact, it might be so weak for the point in which you face it that you might need to equip weaker weapons or remove the Grathnodes from your equipments in order to raise your Harmonics level high enough to obtain all the items it drops. However, don't worry much about it, as all of its drops can be gotten elsewhere.