(otoko mizugi charenji)
Art challenge where a female character is made to wear male swimwear, either jammers or swim trunks, while also topless and in a public space such as a beach or pool. Works best with an androgynous-looking short-haired female character with a boyish haircut and a flat chest or small breasts, but art featuring obviously female characters with longer hair and/or larger busts can also suffice, possibly for definite titillation of the viewer and embarrassment for the subject. Tomboys are frequently used as subjects to emphasize their masculine personalities.
While art of girls in male swimwear have been around for quite some time, the first direct response to the challenge appears to have been from November 21, 2020 on Twitter and Pixiv with post #4212758 (originally uploaded to Pixiv on the said date).
This tag can only be applied for direct art responses uploaded on Twitter or any art site on or after November 21, 2020. While the "男水着チャレンジ" tag is also being retroactively added to art uploaded prior to the said date on Pixiv, Nico Nico, and the like which appear to follow the concept, it is discouraged to do so here since it is highly likely the retroactive tag additions in said art sites are just mere afterthoughts.