Hmm, it's hard to say, 'cause I kinda like everybody, you gotta love how Ryuu is with animals and the twins, the twins are also unique in their own way
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Like the chapter were Megumi shouts
Tadashi is just a hell lot of fun with him being smashed by Akira all the time, Akira is funny with her beloved tea and her attachment towards Hikari, Kei is so cute with his stone-face only breaking when Hikari is in danger and so on, and Hikari is very lovable with her denseness plus she is refreshingly strong and stubborn, instead of all those wimpy, crying usual shoujo heroines. Oh, and not to forget Keis dad
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I love the way the box is saying "Takishimas dad age 35" almost everytime we see him
And
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Sui is also very cute
But if I have to choose it would probably be a draw between Hikari and Kei.
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I sold my soul to The Devil, but now the bastard wants his money back!