The Renka (Love Song) series is currently made up of 5 songs created by Lelele-P. These songs are not connected to each other in any way but shows Len singing in 5 different emotions trying to express his love. The emotions are Heta, Ike, Tsundere, Mase and Yande which are Timid, Cool, Tsundere, Mature and Psychotic respectively. Go to Tsunderenka's page to see Tsundere's meaning.
PS: Some people may use "Lenka" instead of "Renka". Example: Ikelenka
Songs in the series: