---From the Yui+Aqua english patch---
She does not have an "Ayanote" (POKéDEX) description.
Her Ayanote number is 151, so she is "Mew".
Her sprite is exactly the same as Akyuu (#251).
She is unable to learn any TM or HM.
Because the Yui+Aqua patch is NOT 100% complete, I can't get more information about this loli. To get her, you have to use cheats (codes) to encounter and catch her in the wild. If you use cheats such as "Mew in box 1's first slot" then she will not be registered in the pokedex, so make sure to fight and catch her.
Use Firered USA codes.