well the first series ended like that becouse of author's pesonal life problems... which is his wife cheated on him with other dude as he was working on next chapters...and If I remember she took some of his credit cards and such... so generally a marriage problem (harunas char was based on his wife.. so she later demanded money for it in court)
but as the problems were solved darkness series started and its a killa with momo and her plan... as it has a goal in it... which is the harem... in 1st series it was lacking I did not see where it was heading...