I did not intend to enter the fandom this way, but... when this plotbunny attacked, I couldn't resist and this is the result. I hope it's not too out of character.
Disclaimer: Durarara! is the intellectual property of Narito Ryohgo, it is not this author's intention to make any money with this publication.
The way she spoke his name peeked his interest, and he took the effort of turning his chair so he could face her. "I didn't know you'd be back so soon, Namie~!" he said, clearly amused by her anger.
She stomped over to him, leaning dangerously close over his desk – for a moment he grieved over the fact that she wasn't wearing a low cut top, but got over it because even if she was wearing one, it wouldn't be for him. "I asked you to do one thing for me while I was gone, I get back, and what do I find!"
"Is that a rhetorical question?" The smile on his face only managed to infuriate her more.
"You killed my plant!" How a woman could manage to be so upset over an inanimate (though technically alive) object was beyond him. Izaya glanced at the house plant perched on a small table in front of the window, bathing in Ikebukuro's setting sun, where he could peacefully watch the human race go on about their ways. He found it terribly kind of himself to be so giving to share this view with someone (even if that someone was a plant).
"Looks fine to me."
That one tiny comment only set her off more. She stalked over to the plant and brought it back to his desk, shaking it in his face. "What part of this looks "fine" to you!" He turned his head upwards when one of the leaves almost poked him in the eye.
"I guess when you hold him like that he does look a bit depressed…" Namie was trying to find out if Izaya was truly clueless, or if he was being an ass again. Probably the latter, but with him, you never knew. Right now, the way he studied the plant almost made him look silly, as if he was trying to psycho-analyze the poor thing with one look.
She slammed the plant on his desk, the force of it letting dirt spill over the brim. "But he kind of looks the same as when you brought him in," he offered, ending his plant examination.
If possible, she leaned even closer. "When I brought it in, it was green. Not brown."
Izaya stared at her. "If you'd rather have a green plant, I could always buy you a new one." He half-expected her to scream at him again, about how this was a gift from her dear Seiji-kun, for her birthday, nonetheless! – but she didn't do anything of the sort.
She sort of mumbled an okay, and stumbled out of his office, a trail of dirt the only indication she had ever been there. A pity. He had come to like that plant.
Conclusion: Don't give Izaya a plant for his birthday. He'd just forget to water it. ;)