Water
The droplets bead up in her hair, which, by some feat of alien biology, won't hold the water. No matter how wet she gets, and how often she dunks her head underwater, her hair is always springy and lovely, not wet at all.
Shiro, of course, can't say the same for his own hair. His bangs have gotten extraordinarily long and the ends fall in his eyes, irritating, but not quite enough to driving him to cutting them yet.
She props her foot on the edge of the tub and runs a soapy hand down her leg. The sight of it sends shivers of chills down Shiro's spine and waves of heat through his abdomen. She's so gorgeous, even doing the simplest of things, that it takes his breath away.
He can't tear his gaze away from her leg, and she notices. She smirks and drops it back in the water, leaning forward to catch his gaze.
"Are you alright, Shiro?"
"Fine," he answers quickly.
"Are you sure? You seem to be having some rather... human reactions."
His face flushes darkly and he shifts, forcing himself to laugh. "How forward of you."
She purses her lips before splashing water at him. "You're awfully shy for a leader, you know that?"
He smiles at her. "Normally, as a leader, I don't face things quite so intimidating."
"Am I that intimidating?"
"Not you specifically... more like... I can't describe it."
"I think I understand."
She closes the distance between them and presses a lingering kiss to his jaw. He shivers and rests his hands on the backs of her shoulders, dizzy from a lack of oxygen.