Prologue
The colorful extravagance of some birds, the deliberately excessive horns, manes, and tusks of some mammals, the complex courting behavior of many animals, the very existence of sex itself - and by extension the love songs on the radio, and all the love-addled poems ever written - all likely evolved because of parasites, because all organisms must run as fast as they can just to stay in place.
- Moises Velasquez-Manoff
"An Epidemic of Absence"
Kengo Kousaka, who joined a small local systems development company after graduating college, decided to quit a year after coming on for reasons that would make anyone raise an eyebrow. From then on, this would repeat in a similar way almost yearly, and in his rolling about between jobs, he suddenly fell into depression. But he had no awareness of his illness; even at the worst of times, when he was so depressed as to find breathing a chore, even when he suddenly found temptations of death crossing his mind, even when he started weeping at night for no apparent reason, he thought it was all the fault of the winter cold.
It happened in winter when he was age 27. It was a bizarre winter, come to think of it. There were a number of meetings, and a number of farewells. There were happy coincidences and unhappy accidents. There were things that changed vastly, and things that didn't change at all.
That winter, he experienced a rather late first love. It was a girl ten years his younger. An unemployed, depressed young man, and a bug-loving school-skipping girl. It wasn't proper in any sense, but it was undeniably love.
*
"Lifelong copulation?", Kousaka repeated.
"Yes, lifelong," the girl nodded. "Diplozoon paradoxum spend half their lives fused with their partner."
The girl produced a keychain and held it in front of Kousaka.
"This is D. paradoxum."
Kousaka brought his face close and looked it over. Its design was simplified, but it appeared as if it was modeled after a creature with two pairs of wings. The fore and rear wings differed, the fore pair being about three times the size of the rear pair. At a glance, it just looked like a butterfly.
"And despite how beautiful it looks, it's a bona-fide parasite, belonging to Platyhelminthes Monogenea."
"Looks like a plain old butterfly."
"Look closer. No antennae, right?"
Just as the girl said, the creature had no antennae. One could assume they were simply omitted for convenience of design, but the girl considered it an important distinction.
"This actually depicts two D. paradoxum conjoined in an X shape." The girl formed an X with her fingers.
"So since you say they do lifelong copulation," Kousaka said, trying to find the proper expression, "after they conjoin, they're constantly having sex?"
"In a sense, yes. Each one's male sexual parts connect to the other's female sexual parts."
"Each one's...?"
"Yeah. D. paradoxum have both male and female sexual organs. Which they call hermaphroditism. So you might think they could self-fertilize without a partner, but for some reason, they don't do that. They put in the effort to find a partner, then exchange sperm."
Kousaka grinned bitterly. "Talk about luxurious."
"The fact they dare to do with someone else what they could just do alone is kind of loathsome, huh?", the girl agreed. "But there are things to learn from that. For instance, D. paradoxum aren't fussy about partners. As if treating their love at first sight as destiny, they'll combine with the first of their kind they ever meet without any qualms. Also, D. paradoxum don't abandon their partners to the last. Once D. paradoxum join together, they never let go of each other. If you try to tear them apart, they'll die."
"That's why it's lifelong copulation," Kousaka said, impressed. "Amazing. Like a happily-wedded couple."
"Yes. Like birds of a feather, like entwined roots," the girl said proudly, as if one of her relatives was being complimented. "As a bonus, these parasites inhabit koi."
"Koi?"
"Yes - so they're parasites of "love." Isn't that such a perfect coincidence? Even further, D. paradoxum who successfully inhabit a koi discard its eyeballs within 24 hours. So the koi, like love, is blind."
"Love is blind," he repeated out loud. "I never expected to hear such a romantic thing out of your mouth."
Hearing this, the girl's eyes widened like she'd come to her senses, and after a pause, she covered her face.
"What's up?"
"...Now that I think about it, maybe sexual organs and copulation and stuff aren't things I should talk about in public so much." The girl's cheeks faintly reddened. "I feel stupid now."
"Nah, it was interesting." Kousaka snorted, finding the girl's flustering funny. "Keep talking. About parasites."
The girl was silent for a while, but slowly began to say more. Kousaka lent her an ear.