{sonna assari dekiru} mono nanoka そんなあっさりできるものなのか
It's something [that] {can be done so easily}?
subarashii 素晴らしい
Marvelous.
dewa karada no naka wo mana ga guruguru guruguru junkan shite {{oiru} koto no nai} karada ni itashimashou! では体の中をマナがぐるぐるぐるぐる循環して老いることのない体にいたしましょう！
Then, let's make the mana circulate around and around through inside of [your] body, and turn [it] into a body [that] {never {ages}}.
wo を particle - marks the medium through which movement happens.
mana マナ
Common term for magical energy in role-playing games. Also known as MP, magic points, magic power.
oiru 老いる
To age. To grow old.
~koto ga nai ～ことがない
To never [do something]. (to never age).
