I Found It!

Riku revisits her childhood memories after finding an old teddy-bear in her closet. Dark goes to steal a piece from the "haunted" Old Clover Mansion... which is where Riku lost the teddy-bear when she was younger, that it was later rescued by a boy. Riku figured out later that it is Daisuke who retrieved her precious thing, the teddy bear. This teddy-bear was given to her by her grandmother. Risa also was given a rabbit stuffed toy. Risa also discovers a secret close to Dark's heart.

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S01E17 - A Summer Without Dark