Hence, our reincarnated magical "girl" is the only witch who can use ena in the way. Seriously this dude is wild. Capable of soloing both the defense of Earth and the counter invasion of incubi.
The soloing in this context is he defends both Earth and invading the incubi world alone with his power. At first glance this looks like a typical magical girl story. You know the street level conflict of magic girls fighting monsters on a small scale.
However, It's actually a full scale world war and mankind isn't winning. the rest of the world is in a dire state and pretty much only Japan has a functional society thanks to our witch defending it from the shadows. He is the only one capable of fighting the incubi on full scale war level because of his self replicating insect/invertebrate army both on Earth and the incubi world (the insect army is pretty much at legion strength over that side too) While the witches (from especially Japan) are very powerful individually and some of them can use familiars in a combat role. None of them fight incubi in a full scale open war.
Granted our dude has limitations. His insects have a very simple friend or foe IFF system (murder incubi), can't deal with human traitors/mind broken witches, gets overwhelmed mentally due to the sheer information from his legions
(especially after he goes full ham in Korea, China and the US)
and operates in Japan from the shadows because of the sheer brutality the insects inflict on incubi to prevent mass panic. Amongst all the witches he is also the weakest one physically. Though, good luck trying to get your incubi ass close before getting ripped apart.
Hence, the other witches fill the gaps for him. Like dealing openly with incubi that slip past his insects into the open, black ops work (AKA murdering traitors both human and witches) and sharing the mental load of his insect/invertebrate combat reports