So, Suika vs Ahriman...
For attack potency, we see Ahriman sitting at least Moon level, just with his physical abilities, while his actual AP with his magic and other stuff is much higher due to most of his abilities ignoring durability, such as biomancy, enfeeble, as well as telepathic abilities such as dominate and psychic shriek, both of which ignore durability completely as well as attacking the mind. Suika, looking at her abilities list, has no defense against mind attacks at Ahriman's sort of caliber. Suika's physical abilities also pale in comparison to Ahriman, where she only sits at Mountain level compared to Ahriman's Moon level.
However, here is the issue in question. Ahzek's actual movement speed is only FTE, with FTL reactions and attack speed. This probably means that even though Ahriman can react to anything incoming at him that moves at things faster than light, could Ahzek's body move fast enough to keep up with his reactions?
Comparing movement speed wise, Suika is at least ~100000 times faster compared to Ahriman, if Suika was sitting at an absolute minimum in terms of relativistic speed and if Ahriman was sitting at an absolute maximum of Subsonic+ speed. To Suika, she sees Ahriman's movements as practically borderline standstill.
I am also reading that Suika can fight evenly with Yukari, which means that Suika is comparable to her (although Yukari may have been holding back?)
In short, if Ahriman does not get overwhelmed with Suika's attacks at the first moment in the fight, Ahriman's vast range of abilities nets him the battle. However, Suika has the ability to reduce the density of materials via (Manipulation of Density and Sparseness). If I am reading this correctly, Suika can reduce the density of anything that she wants to, meaning that Suika can likely reduce the durability of Ahriman to the point where her physical attacks can shred Ahriman apart, although Iron Arm may reduce this to an extent.
Now, for the finale, for most of Ahriman's lethal abilities, does he have to move his limbs to cast his spells/abilities, or can he perform them with his thoughts? Precognition and divination abilities are not very helpful if the opponent has that much of a speed gap, meaning even though Ahriman can react to Suika's movements, his body will not keep up with his reaction speed, therefore, Ahriman is going to get blitzed to hell and back (unless Ahriman can perform his time stop).
I am probably going with Suika here, especially if her durability is comparable to Yukari's because Suika is:
- 100000 times faster than Ahriman movement wise
- can reduce Ahriman's durability via density manipulation
- seeing Ahriman's movement speed at a borderline crawl, meaning Ahriman gets blitzed before he moves any part of his body
Not sure about both of their characters personalities though, perhaps that can tip the edge to Ahriman somewhat?