Honoo no Haramase Tenkousei

Both titles are about the protagonist hunting down for one girl after another in a non-aggressive matter, so both titles are free of any dark tones and the characters are in mutual agreement giving the titles a light-hearted tone.  

Both are hentai with three episodes about a guy that tries to sleep with as much women as possible. Both are harem genre, but 15 Bishoujo Hyouryuuki is more comedy.