He's a shy and quite quiet boy that's at Empty Sekai. Sekais are created with a person's feelings, in this case, Mafuyu's feelings (Helping her to find her true feelings) 
Len uses to have an insecure relation with all of the integrants (Mizuki Akiyama, Kanade Yoisaki, Ena Shinonime And mafuyu Asahina)
 He has a sister named Rin Kagamine, she's strict or tsundere sometimes... Meiko is almost the same, a serious person, and Kaito, Miku and Luka Megurine
There are more sekais
