Natsu no Arashi! Akinai-chū (TV)

In ep 2 in the scene where Jun is being chased by Hajime you can see School Rumble characters in the background dressed in the onsen yukata.

In ep 5. Jun is cosplaying from Sailor Moon as Tuxedo Mask.

In episode 1 at 18:59 Arashi thinks that Jun transforms into a boy when splashed with water. This is a reference to Ranma 1/2 when the main character is splashed with cold water he changes into a girl.

In episode 3 at 20:09 there is a reference to the movie ET when Hajime and Arashi jumped in the sky on Hajime's bike.

In episode 4 at 13:01 Kaya tells Hajime to look out the window to see a skyfish. This is a reference to Eureka 7.

In episode 8, during the cave scene Yayoi is dressed as Indiana Jones. This is also a joke on Ai Nonaka's past voice roles in Shaft animation's animes. (Konoka from Negima!? Ichijō from Pani Poni Dash!) as they all at some point have dressed in the same clothing.

In episode 13 at 4:37, Kaya is dressed in Tenma's school uniform from School Rumble as she drinks the spoiled milk.

In episode 13 at 6:45, that guy who is constantly asking for salt(shio kudasai) each episode finally gets it.