Dangerous Swimsuit originates in the MSX version of Dragon Quest 2. If you speak to the king on the second floor of the weapon shop in Radatoum while the Princess of Moonbrooke is equipped with no items he will give you the swimsuit. While it does not change the appearance of the character, it does give a short splash screen of the swimsuit, as shown below. It's also very powerful, as it causes monsters to fail their attacks due to distraction (including bosses).
Pervy old man!KotoneBut why is it that we still can't change player costumes!?You've been playing too much Dragon Quest 9!I want to make her journey with the Dangerous Swimsuit.The eagerly anticipated remakes HeartGold and SoulSilver are finally out...Kotone has equipped the Dangerous Swimsuit.