So... how is this bdsm?

The "bondage" tag implies "bdsm," even when it's artistic and wouldn't be very functional as actual restraints, as in this picture.

Adding the tag "slave" too is pretty silly, though. I mean, you could argue that the Angeloids are slaves, but they're not what someone searching that tag is going to be looking for.

7HS said:
The "bondage" tag implies "bdsm," even when it's artistic and wouldn't be very functional as actual restraints, as in this picture.

Although the wiki doesn't reflect it at the moment, this is among the things that tied is for.