Total Recommendations: 3
-Both have a circus/amusement park theme. -Both include mutants/hybrids. -Both are quite dark, although DW is more explicit.
Both have inhuman girls with gigantic bazookas who choose a random boy as their "master," and upon imprinting grow misty-eyed and kiss the helpless male protagonist. Said inhuman girls insist they stay at the home of their "master", and said masters don't know what to do with themselves. Sekirei has more ecchi than DearS, and has a better storyline - however DearS is a lot more cute and colorful.
Both male protagonists speak very similarly, both have a slice-of-life setting, are set in high school, and include school clubs and their maintaining of them. However, Haruhi is more outgoing and humorous than Clannad, whereas Clannad is more sweet and easygoing than Haruhi.