To provide a method for writing and erasing without problem in a circumferential contamination or health with a dust or the like by eliminating a skip or unevenness on a writing image even by rapidly writing in the case of writing a whiteboard or the like, and completely erasing in the case of erasing a written image and an ink and an eraser used therefor.

An ink obtained by dispersing one or more types of dyes selected from a dye represented by a general formula (I) D-(X) (wherein D is a compound having a chromophore or a group derivated from the compound, X is a dissociative proton bonded directly to D or via a bivalent bond group or a group having a dissociative proton, and y is an integer of 0 to 7) in water is used, written, and the written image is erased by an eraser containing at least one type of reducing agent and water. Thus, since the dye is dispersed in a dispersion medium containing the water as a main component, an absorbing efficiency of the dye is improved. Even in the case of rapidly writing, a skip or an unevenness can be prevented.