User blog comment:Hitsuji Mamoru/Servant Creation Room 2 : Guess of the Who/@comment-31726296-20170609230836/@comment-31726296-20170611205225

12.7cm???? Oops that was not meant to be it. My bad, it meant to be 152cm not 12.7cm. Thanks FGOHikaru for catching that and you are the best. Also Magical Girl Lyrical Nanoha is the series. However, it's not any one from the main cast. Meaning Nanoha, Fate, Hayate, Vivio, etc are not Ruler.

A hint is that Ruler is related to someone from the main cast. love this helps.

P.S I will wait for my FGOXMGLN Event to come and will wait for Heroic Spirit Nanoha and Fate to be Summonable.