‼️‼️Modern scholars say that this story was made up: there was never an ancient god named Kupala/Kupalo; later created in late-folklore notes and romantic-era retellings. Once you add a millennium of Christian erasure…we’re left piecing the myth together from russian blogggers, Wikipedia articles, and the odd Reddit thread.

Treat this story as a legend we hope is anctual Slavic lore.

☀️ The Longest Day

On the Summer Solstice (year’s longest day), with the sun refusing to dip below the treeline, Simargl—guardian of seeds, sprouts, and tender roots—joins Kupalnitsa, velvet-soft mistress of night, to welcome their newborn twins:

Kupalo, a boy with sparks in his eyes, forever chasing the nearest flame.
Kostroma, a girl who carries the hush of rivers in her heartbeat.

At dusk, Perun, the god of thunder strides into the clearing, laughter rumbling like distant storm clouds. From his cloak he sets down an ember-bright fern flower (kwiat paproci), said to flare open for only a single heartbeat each midsummer midnight. (More on that impossible blossom later.)

Ivan Kupała, fern flower. (Ukraine stamp), 1997 (Kwiat Paproci)

🎶 Two Songs, Two Paths

The twins grow tall in the rye fields, spending childhood afternoons racing dragonflies and skimming stones across the Volga’s glassy bends. Their laughter is as steady as the river—until one violet evening, when two voices drift out of the sky:

Alkonost sings first, a ribbon of sound sweet as daylight and honey, a tune that makes wheat heads sway as though they’ve heard good news.
Sirin follows with a low, aching melody—folklore says her songs are so heavy with sorrow they can carry a listener’s heart into the otherworld.

Alkonost’s joy draws Kostroma closer, step by careful step. Sirin’s darker call tugs at Kupalo, and he follows without looking back. He walks past the last stalk of rye, past the treeline, until the ground beneath him thins into Nawia, the shadowed realm below.*

By sunrise he is gone, and Kostroma is left alone on the riverbank—listening for a brother who no longer answers.

*Kupala and Kostroma (2015)* *Andrey Alekseevich Shishkin*

🌿 The Wreath and the Wind

Seasons roll on. Kostroma, now a quick-witted young woman, spends her evenings by the river weaving wianek crowns (a maiden’s virginity badge in old Slavic custom).

She settles a wreath of herbs and wildlowers on her head and laughs:

“Not even the wildest gusts will knock this off—so no man will, either.”

The gods hear the dare. A sharp squall barrels through the rye; petals scatter, and the crown lifts like a tiny boat, sliding onto the moonlit current.

Far downstream, Kupalo—finally escaped from Nawia—rows a simple boat. He spots the drifting flowers, scoops them up, and recalls the village rule every child knows:

Whoever rescues a maiden’s wreath must find its maker and marry her.

They meet on the bank moments before midnight. Sparks fly. Neither guesses they are siblings, yet the pull is instant, deep, and—by custom—unchangeable. They marry that very night beside a roaring bonfire, believing destiny has smiled.

🕯 Truth at Midnight

The new couple sit by the fading fire, whispering plans for dawn. Embers lift on the breeze, and the river offers only its quiet hush. Then—as if the night itself yields to a higher will—the wind stops. The gods, unable to keep the secret, let their verdict fall:

“Kupalo, Kostroma… you are brother and sister—twins.”

Horror locks their hearts. Kupalo’s eyes freeze on the glowing coals; Kostroma’s on the mirror-dark water. Moments earlier their pulses raced with joy—now they hammer with dread.

Kupalo rises and steps into the embers, the flames rising to meet him with a roar. Kostroma walks to the river’s edge, slips beneath its silver surface, and the ripples flatten, leaving the bank silent.**

In some tellings, Kostroma does not truly die. Instead, she becomes a mavka (rusalka)—a restless lake-spirit. Night after night she wanders the shore, enchanting young men and pulling them into the depths, mistaking each victim for Kupalo until she realises—too late—that the drowned stranger is not her lost twin.

*Mermaids (2015)* *Andrey Alekseevich Shishkin*

🌸 A Flower for Two Hearts

Regret drifts across the clearing. To bind the twins without breaking the world’s order, unseen powers weave their souls into a single wildflower—yellow petals bright as flame, blue petals deep as river. At dawn a lone bloom stands where fire met water, named Kupalo-da-Mavka***.

And so, each Noc Kupały, (Kupalo’s Night) wreaths still float down quiet rivers, bonfires leap toward the stars, and somewhere—so the tales insist—the elusive fern flower flashes to life for a single heartbeat before the forest swallows it again.

*Other versions of the story drop Alkonost altogether. “On the day of Kupala, the bird of death - Sirin - flew to the Ra River. She sang wonderful songs. But whoever listened to her - forgot about everything in the world and followed Sirin to the kingdom of Nawia. […]Fate separated the brother and sister. The baby Kupala, by order of the Lord of Darkness, was carried away to the ends of the earth by geese-swans and the Sirin bird.”

**One version ends with the lovers learning the truth, clasping hands, and leaping together from a cliff into the river rather than parting by fire and water.

***Christians later renamed Kupala de Mavka flowwer to Ivan-da-Marya, Kupala was switched to Ivan the Baptist, and Mavka to Maria, after the Virgin Mary.)