Kono Naka ni Hitori, Imouto ga Iru!, Nisekoi Recommendations
-Both about a boy trying to find out who his "forgotten" companion is
-The atmosphere is similar in both (Light-hearted, and very short scenes of plot progression
-Both are harems
-Both take place in a school setting, both Nisekoi and NAKAIMO are realistic Slice of Lifes
-Nisekoi focuses a bit more on comedy, NAKAIMO has other things such as fanservice and ecchi
They're both traditional harem series where the MC is from wealthy and powerful family. Nisekoi is less ecchi than KNHII.
In a harem comedy anime, one major problem writers have to overcome is how to maintain the "harem" situation, since in normal circumstances any such arrangement would quickly collapse.
Most harem comedies do this by making the protagonist or the girls (or both) defective in some way (stupid, socially inept, etc.).
One of the reasons I like Nisekoi is that (while some of this is still present), there are more complex plot devices at work which which sustain the harem (the question of the childhood promise and the need to fake a relationship to avoid a turf war).
Kono Naka does this