Riru is an incredibly weak lesser demon with a penchant for clinging to those that interest him.
He's parasitic when he does so, feeding off of various energies of his heart's desire; he doesn't mean to, but it's how he survives, and his need to 'cling' to others is his means of living, and something that draws him in.
It's within his powers to appear attractive to whomever interests him, but whether he is successful is another story entirely, mostly due to his low dark magic strength. He is weak physically as well as magically; everything he does is for looks rather than actual capability, not that he'd admit it (unless demanded to).

He is shy despite his nature of needing others, and needs a lot of confidence borrowed from whomever provides him with his energy. Most of his looks come from an overcompensation on what he imagines confidence looks like.
And though he is dedicated to others, Riru is not entirely as subservient as his nature should have him be, mostly just an emotional pushover rather than obeying any and every word by his (current, whoever that may be) desire. He has little need to be confrontational, and instead works better with a stress-free relationship, making for no distractions when siphoning energies.