Well, you could always... make the black semi-transparent I guess. Before I go on though, it is possible to achieve the original sprite you were looking for, but you'd be forced to use the robe slot (this is what FXFreitas's meant, I think). For more info : https://rathena.org/board/topic/72734-guide-custom-wings-at-robe-place/
You could make the sprite semi-transparent, it would look like the following (³²_kaura1) :
If you use a semi-transparent gradient though, you might be satisfied with the result (³²_kaura2) :
Side note, the walking frames for top right are somewhat off.
Kiel Aura 2015.rar