They are characterised by having a /k/ in the first person singular pronoun "I/me", as opposed to the Southern Eastern Sudanic languages, which have an /n/.
Nyima has yet to be conclusively linked to the other languages, and would appear to be the closest relative of Ek Sudanic rather than Ek Sudanic proper.
A reconstruction of Proto-Northern Eastern Sudanic has also been proposed by Rilly (2010).
[1] Rilly (2009:2)[2] provides the following internal structure for the Northern Eastern Sudanic languages.
Based on morphological evidence such as tripartite number marking on nominals, Roger Blench (2021) suggests that the Maban languages may be closely related.