Okay, the title of this comic is "Wachiki-chan wa Yurusaretai" (Wachiki-chan Wants to be Forgiven), she calls herself Wachiki throughout, and everyone at the 2ch thread where some of this comic was posted is calling her Wachiki.
Could Wachiki be some kind of Kogasa variation with horns?
I've been searching/browsing Goo, Pixiv, the atwiki anko mirror, etc, and I'm seeing numerous references to Kogasa using "Wachiki" (an Edo-era feminine variation of "watashi") to refer to herself, and variations on the catchphrase "Wachiki yurus___" (I [am/will be/have been] forgiven.)
The argument _against_ it being Kogasa... is the way Wachiki looks, obviously. I browsed lots of Kogasa pics on Pixiv, and she didn't have horns in any of them.
The closest thing to a Kogasa with horns I've seen is the artist Wachiki-aki, who draws himself(?) as having a Kogasa-like head (blue-green hair, odd eyes), and two umbrellas as horns. post #29994post #30851 (He's not identified as Wachiki-aki at OYP, but I saw some of his art under that name at http://loda.jp/otaku_13854/?id=370)
But with Kou's art style, you'd think he'd give the horns some umbrella-like detail or shade in one eye if he were drawing Kogasa.