The Magatsu Kyuubi is a Psion, a corrupted version of the Kyuubi and has the ability to create intangible orbs on the field that decrease the maximum HP of all God Eaters in the affected radius.
According to the title of the mission in which it is faced, the Magatsu Kyuubi is one of the earliest known Aragami, its Retro Oracle Cells indicating a very early birth.
The following information is taken from the official in-game descriptions of the Aragami found in the NORN Terminal's database.
God Eater 2 Rage Burst
An effective way to avoid it using its HP reduction is to hit it several times when downed, then let AI teammates do the rest. When it's about to get up it usually becomes Enraged and sends out the black hole; use Stun Grenade right away when it stands to stop it from doing so.
Although Magatsu Kyuubi's resonance ability reduces max HP, having lowered HP does not count as a hit for the purpose of a no damage/perfect run (the player must actually be hit by the aragami in the mission to break the "no damage" clause).
Killing the Magatsu Kyuubi when the orbs are out will cause them to disappear immediately.
Once its HP are low enough, Magatsu starts using its Resonance effect; start surround itself with a damaging dome (not 1 hit only like other dome-like attacks) and start firing large laser similar to Arda Nova's/ Tsukuyomi's around it with the same pattern everytime.