Uke

From the Japanese verb 'ukeru' (receive) it's used in anime, manga, doujinshi and fanfiction for the "bottom" or "passive" in a yaoi/shounen-ai (male/male) relationship. 

The Uke is often (but not always) the younger of the two/ shorter/ less experienced and more 'cute' than handsome, though they can be (and many are) both. He can be sweet and peppy or pessimistic and of low self confidence or tsundere. Can be innocent or dirty minded, It all depends. They usually get flustered very easily and have larger eyes than their partner.

A very innocent (well twords the beginning that is 😏) Uke is Izumi from Love stage. He is shorter than his Seme, Ryouma, and has larger eyes than him as well. Izumi is so cute and girlish that when the female child actor doesn't show up for a wedding commercial they put him in a dress and give him pigtails and no one, including Ryouma, is the wiser. Even years later Izumi is still so girly that they put him in a wig and dress again and it still works.

A more Tsundere Uke is Romano/Lovino from Hetalia. He curses a lot and calls his Seme, Spain/Antonio, names like Tomato Bastard. He get easily flustered, and when he does, Spain likes to compare him to a tomato. Pretty sure both of them have a serious Tomato fetish.