Dusa

Dusa is a shade in the form of a floating, disembodied Gorgon's head. She works as a maid in the House of Hades, constantly floating around and cleaning.

Affinity

If given Nectar, Dusa will give you the Harpy Feather Duster. After being given 6 bottles of Nectar, further gifts will be locked until her favor is completed. Completing the favor and gifting her a bottle of Ambrosia will have her give you Companion Fidi in return.

Favor

Dusa's favor involves the lounge renovations, which she has fallen behind on doing. Zagreus must help her bring the lounge up to Nyx's standards by using the House Contractor to complete a minimum of 12 Lounge-focused renovations, which must include at least one rug for the area as well as cleaning up Cerberus's fur and the scratches he left in the floor. Doing so will complete the A Place of Revelry prophecy and unlock the ability to give Ambrosia to Dusa.

Romance

Dusa's romance differs from the other options in that each successive gift of Ambrosia requires an increased number of bottles; while her first only requires 1, subsequent gifts require 2, then 3, until her final gift is given as 5 bottles.

After giving Dusa the tenth gift, she and Zagreus will have a conversation where Dusa explains that she has come to realise she isn't looking for an intimate relationship, and isn't attracted to him in that way. They agree to remain "friends for all eternity" instead, though as Zagreus points out, that in itself can be its own form of love.

Some time after the final romance conversation, Dusa will offer to return all the Ambrosia she has been given; Zagreus may take them back or persuade her to keep them as the gift they were intended as, with no negative repercussions for either choice.

Dusa can be romanced at the same time as Megaera and/or Thanatos with no drawbacks.

Codex entry

'...A splendid House such as the Master's own requires a great deal of cleaning, and the little gorgon seems forever doomed to do it all herself. I sometimes offer my assistance, although it is here the little gorgon bares her fangs, refusing any help. That I can clearly see my own reflection in our polished countertops suggests she doesn't need it, either. Although she comes off as talkative, to my knowledge she has never been forthcoming about the circumstances that led her here. A background check confirmed she has only trace connections to the gorgons of Asphodel, though could not verify any connection to the notorious gorgon-sisters of the surface. The Master deemed further inquiry into this unlawful, and granted supervisory responsibilities to Nyx, who ensures the gorgon's workload is always full. In turn, the gorgon steadfastly accomplishes her duties, with diligence if not grace, perhaps finding pleasure purely in a job well done.'

Additional notes

For additional information on Medusa that does not pertain to Hades, see Wikipedia's article: Medusa

Dusa's position as a maid in the House of Hades is a play on the name Medusa - she is Maid Dusa.
She seems to have a crush on Zagreus, emitting a gasp and several hearts whenever he gets close. Her conversations are short and flustered, and she often flees into the rafters afterwards. As of the Long Winter update, this relationship can be explored in further detail.