Nao Tomori (Charlotte)
Ayumi Otosaka (Charlotte)
Tatsumaki(One Punch Man)
Sora Kasugano(Yosuga no sora)
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High School DxD:-
Rias Gremory
Akeno Himejima
Xenovia Quarta
Irina Shidou
Koneko Toujou
Rossweissei
Grafia Lucifage
Kuroko
Asia Argento
Ravel Phenex
Sona Sitri
Serafall Leviathan
Gabriel
Kalawarner
Yasaka
Tsubasa Yura
Tsubaki Shinra
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Rosario+Vampire:-
Moka Akashiya
Mizore Shirayuli
Kurumu murini
Kokoa Shuzen
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Sun seto (My Bride is a Mermaid)
Lunar Edomae(My Bride is a Mermaid)
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Chitoge Kirisaki(Nisekoi)
Marika Tachibana(Nisekoi)
Seishirō Tsugumi(Nisekoi)
Haru Onodera(Nisekoi)
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Yuuki Asuna (Sword Art Online)
Kirigaya Suguha(Sword Art Online)(Kirito's sister)
Asada Shino(Sword Art Online)
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Akame(Akame Ga Kill!)
Kurome(Akame Ga Kill!)
Chelsea(Akame Ga Kill!)
Mine(Akame Ga Kill!)
Esdeath (Maybe or may not be)
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Shizuka (Doraemon)
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You can suggest some more harem candidates for this fanfic
of course, there will more candidates for his Harem along his journey!!