Washable Tokyo Soir form forma All-in-one Black Formal

I just bought this 2 days ago to wear for a Buddhist memorial service and a wedding, but the plans have suddenly changed and I won't be able to wear it. I'm hoping someone else can use it.

When I bought it, the store staff brought out a new one from the back, and I haven't even tried it on yet. The store staff mentioned that it can be washed with an osharegi (fashionable clothes) detergent.

For reference, I have a very bone-straight body type, am 154cm tall, and quite overweight. I tried it on with heeled sandals that are commonly found in stores, and the sales associate complimented the flattering silhouette. I suspect the bow tie at the collar and the waistline might suit a bone-straight body type.
*Necklace is not included.