Arc "Nero" Naginata's Links
As far as Arc knew, Luna is the monster that brainwashed him. Now, as Nero, he loves Luna and his real form, Xenon Naginata, who he calls "Father".
At first, Luna felt an almost seething hatred for Arc, but that was before he brainwashed him and turned him into his "obedient, good little boy". Naginata (Luna) often takes on a more female form around Arc, to treat him with a twisted, motherly love through more maternal actions like breastfeeding.