Actually, her title is "The mature fairy" the idea spun of from the PoFV Cirno plot, where Shiki tries to warn Cirno that even fairies pass on eventually, and that she should shape up and start being more cautious of what she does. It doesn't work with Cirno, but it does work for Keroko, who now has the 'fear of death.' As a result, she becomes much more mature, and as a bonus more powerful than the average fairy to boot.
Lunarians have superior technology, but refuse to share. Add to that their arrogance and Keroko would have jumped on board with Yukari had she lived during the time of the first Lunar war.
In other news, I'm currently working on Fairy!Keroko too.