Fiel Nirvalen

Fiel Nirvalen (フィール・ニルヴァレン, Fīru Niruvaren), who usually has her name shortened to Fii, is an Elf girl who is Chlammy Zell's game partner, as well as the one who helps her cheat using her elven magic. Despite her young physical appearance, she is actually around 52 years old.

(Source: No Game No Life Wiki)