Encyclopedia Entry
There is much remaining ancient lore regarding the great fiends of flame known as "Balrogs", who were once monstrosities said to take in and store vast quantities of flame mana from volcanoes, which would overflow, wreathing their entire bodies in hellfire that could incinerate all their enemies. These beings were always raging with fury and rampaging with tremendous might like all consuming flames, but they were also excellent warriors who could change flames into the shape of swords and skillfully wield them in battle. Their burning tails were sharp and long almost like whips, and just one swing could scorch and hollow out a mountain.
In the present, although they are great fiends who rule volcanic strongholds, they have transformed into hedonistic monsters who like to dress up and spend time hanging out in town with their "Pyrow" minions, but their greatest joy of all is to get it on with the man they love. They say their former fury lies dormant, but they are just as fierce and impulsive as ever, and immensely covetous as well, for whenever they want something, they always have to have it, and they do whatever they want. What's more, these extremely arrogant and proud great fiends boast of themselves being women of the highest caliber too and as such consider that a suitable husband must be among the greatest of men to be a proper match. After verifying what their husbands were actually like, it turns out they were mostly famous individuals, and men of excellence with exuberant personalities, adored by countless people and monsters, who naturally become the center of attention... A balrog's husband is invariably that sort of man. When interacting with her beloved husband, a balrog's pride as a great demon goes out the door, and she'll surrender herself to the man as a passionately fawning lover and just become immersed in the joy of being desired and made love to.
So then, you'd expect that the husbands they choose would already be champions, heroes, or successful men accomplished in various fields, but that doesn't necessarily seem to be the case. To provide an actual example, I'll record a story told to me by the husband of a certain balrog, a man famous for ruling as the king of a certain volcanic kingdom on behalf of his utterly hedonistic spouse. One day, a beautiful woman casually called out to him in town. Soon, they were joined. It turned out that the woman was none other than a balrog, but at the time, the man was merely the second son of a small bakery in town, in other words, apparently, he was an extremely average youth. At the time, he certainly was average, but according to him, from the very moment he met her, "it felt as if something was flaring up from deep within." The force of the raging flames easily pushed him to overcome all the fear, bewilderment, and resignation. Never would those flames smolder out, not even after his many repeated failures. That is what gave him the passion to claim the woman he had fallen for as his own and motivated him to become the kind of man that anyone would recognize as king through days and days of training. Even now, the flames have yet to die, instead, raging even more violently, providing an endless font of vigor. Thanks to that, the man never tires, and with that overflowing energy, a seething lust wells up with endless stamina. Especially, after finishing some task he was supposed to do, or whatever. When there would normally be a desire for rest, instead, an urge so powerful it must be vented or it would drive him crazy comes over him. And always in attendance at his side, repeatedly tempting him provocatively as if to fan that urge and direct it towards herself, is his lover, enraptured and ready to surrender to his embrace, anticipating the moment she'll be carried off to bed which could happen at any time. Whereas before he would've never even thought about approaching a woman, now he can't stand to go without doing her, and whenever there's free time, they spend it engaged in sex. I asked several other people, but this phenomenon of mental and physical invigoration is seen in all men chosen by balrogs.
Through scholarly research, it was discovered that balrogs are monsters that serve the role of controlling volcanoes to prevent eruptions by taking the mana overflowing from volcanoes into themselves and releasing it outside. It's likely that in antiquity, balrogs released it by going on rampages. But in the present, that ferocity... that is to say, going berserk as previously described due to an excess of energy, is entirely unheard of. So then, how do they currently release it? In other words, this suggests not only do they imbue themselves with vast quantities of mana taken from a volcano, they also infuse the men they chose with it. These highly desirous girls always choose the men they love, and always get them. What's more, they wish for the men they love, the men they chose, to become "one of the greatest of men, to be a suitable partner". And if so, then that too is "inevitable".