Jahnu went to Hogwarts in 2010. Same time with Fred Weasley II. He was sorted into Gryffindor. Soon Jahnu became friends with his classmate Fred. Jahnu doesn't joined to Gremlins, because he is a "Kind-Boy".
Jahnu was crushing on Dominique Weasley. Dominique was one year older than him. Jahnu doesn't tell Fred, because Dominique was Fred's cousin.This is not true,because Jahnu actually liked Fred,and was helped by his cousin Oral Patil-Brown.