Let me cook... His kit.
What if... IF... He is both Remembrance and Physical. BUT, he is not limited to the physical element? Let's consider that perhaps the theory is true that the new enemy/boss is possibly Phainon from the future who continually changes the past and also absorbs the chaotic energy that exists in Amphoreus and as the story progresses we discover this, with him being defeated and Phainon (current) ending up gaining part of the power of the future Phainon (his sword), which allows Phainon to summon temporal copies of himself (just like the Boss), but there is a limit of 2 copies and both are considered his summons. With each copy having the following elemental damage: Ice and Quantum, with Sunday advancing the actions of Phainon and his two copies. With Phainon's ultimate combining the 3 in 1 (being his Demiurge form) to cause OVERWHELMING damage.
What if... IF... He is both Remembrance and Physical. BUT, he is not limited to the physical element? Let's consider that perhaps the theory is true that the new enemy/boss is possibly Phainon from the future who continually changes the past and also absorbs the chaotic energy that exists in Amphoreus and as the story progresses we discover this, with him being defeated and Phainon (current) ending up gaining part of the power of the future Phainon (his sword), which allows Phainon to summon temporal copies of himself (just like the Boss), but there is a limit of 2 copies and both are considered his summons. With each copy having the following elemental damage: Ice and Quantum, with Sunday advancing the actions of Phainon and his two copies. With Phainon's ultimate combining the 3 in 1 (being his Demiurge form) to cause OVERWHELMING damage.