Narmaya's Black Butterfly costume?

[ANTARES]

When and how is it going to be able to purchase?

[Sleepy Cyb]

It should be a reward for the upcoming battle pass which should drop the same day as Lucillius, so on the 16th, next week.

I don't think we got any info on how the battle pass will work, whether or not you have to pay for it (Let me fool myself a little longer) or if the battle pass rewards will be available though other means.

EDIT : Seems like the first GBVS had a similar system with a free battle pass which would give you card design for you profile, and a premium battle pass which would give you those sweet weapon and character skins.

So yeah, pretty sure it will work just like that for Rising.