Okay. This is vitally connected to the Berry Song.
As I noticed that there is a (seemingly) White Karelian runosong which states that a Lord and a Lady (I assume Virankannos and Päivätär) decided to make a "fiery son" and have an Underworld maiden give birth to him by being impregnated from eating a berry, I started wondering if there is something that supports this in Finnish runosongs... Yes there is!
In a precious Kainuian runosongs, it is described that Lemmäs, the fiery Underworld maiden, gave birth to Panu, the fiery son. While the beginning part of the conversation between a Lord and a Lady are not included, we can assume the events happened the same as all the circumstances support it. (Mainly, fire being called the creation of Päivätär and son of the world pillar). Another Kainuian runosong states that someone named "Syvätär" gave birth to fire; the name and her role seems to be a corruption of Syöjätär and Louhi, both also Underworld related female figures. It is often said that John the Baptist refuses to baptize the monsterous children of Louhi, but here he gladly names Panu. Who could the name-giver have originally been before Christian influnce? Well, again, White Karelia suggests it was Ukko Virankannos himself.
This clearly explains how fire can be a creation of Päivätär but born from Lemmäs at the same time. Is Panu the same as Lemminkäinen? There is a real tangible possibility for it! Tietäjät wanted to use the name "Panu" for fire in incantations as it was believed to be more powerful.
Kainuian runosongs also put the events of the Origin of Fire, where fire falls from the heavens, to happen after this runosong below. The first two lines are not a part of the original runo but come from Central Finland and South Savo. Why did I include them? Because the woman who gets pregnant from eating a berry in the Berry Song is called Marjetta. These other lines show that she, also known as Margetta (Christianized names), has a real connection to being an Underworld maiden.
 Margetta matala akka Lyhyt akka, Tuonen tyttö Höyhennys Panuttaria Lemmäs laukahattaria Kohun kanto kaksikuisen Jopa kuullen kymmenelle Pantihin kavon kipuja Immin tulta tuikattihin Juoksi vyöstähän vetehen Sukkarihmasta sulaan Vyölapusta lainehelle Kengän kauvolta veteen Siinä pojan synnytteli Synnytteli, kasvatteli Ei kärsi käsin ruveta Eikä koprin kuonnotella Lakin laski polvillensa Lakin päälle lapsen laski Siinä kanto kastehelle Siinä ristillen riputti Johannes parahin pappi Joka on Panun ristinynnä Yöllä piiloteltavaksi Päivillä pidettäväksi Panu parka, Tuonen poika Kirnusi tulisen kirnun Säkehisen säilytteli Pukemissa puhtahissa Valkehissa voattehissa | Margetta, low woman Short woman, girl of Tuoni Höyhennys is a Panutar / Your feathers of Panuttaret Lemmäs is a laukahattara Carried a womb for two months All the way to the tenth month Was the pain of the maiden set The fire of the virgin was flamed She ran into water by her waist Into the melted one by her sock straps Into the waves by her belt Into the water by the shoe's vamp There, she gave birth to a son Gave birth to, raised One could not touch him with hands Nor lull with palms She put a hat onto her knees And lowered the child onto the hat There, she carried him to be baptized [Same again with different words] John, the best of priests Was the one who named Panu To be hidden during nighttime And be held during daytime Poor Panu, son of Tuoni Churned a fiery churn Kept a shining one In clean apparel In white clothes |
We do not know for certain if she has the name "Höyhennys", or if she has feathers of fire. We don't know what kind of hattara (Underworld goddess or demoness) she is as while lauka can mean "low", the line varies widely in oral tradition. Eemil Nestor Setälä thought it comes from lauvas "stream", while Kaarle Krohn pointed out lenkka "an unstable creature". "Panutar", a feminine term for fire, would also be one of her names.