What's with this up-tilted head posture?
It's known as the 'Shaft head tilt' as the animation studio "Shaft" are well known for including it in their shows:

 


Above are other shaft shows; Puella Magi Madoka Magica ,Arakawa Under the Bridge
, Nisekoi.

Anime director of Shaft since 2004, Akiyui Shinbo is responsible for this studio trait. 

knowyourmeme - Shaft Head Tilt

The tilt is merely artistic, with no special meaning. Along with this, Shaft have other signature style traits such as large expansive empty rooms for dramatic effect and fast displaying text. 



(who needs all that space to brush their teeth or have a bath?)

TVTropes Shaft Studio