It was reported that Billlie's Moon Sua had stopped by the memorial space for her brother, the late Moonbin. It was revealed that she had quietly visited and left a letter to her brother, bringing fans to tears.

On April 24, photos of Moonbin's memorial space prepared by Fantagio were revealed on a popular online community. 

A netizen who visited the memorial took photos of the letters written by various visitors. Among them were letters written by Moon Sua.

Sua's letter has brought many people to tears as she wrote, "Oppa, it's me, your one and only precious sister Sua. I came to visit (the memorial) too. I cried so much so I'm going to stop crying now. I'll smile more now. I'm going to do what I want to and be happy. So, I hope you are going to be happy there. Please watch over your sister, if I'm doing well or now."

She continued to write, "I'll live diligently for your sake too. Don't stop me. Still, if things get hard, I'll come to you to vent out so you have to comfort me. You've worked so hard until now. I love you so much and I'll forever be your younger sister. Moon siblings forever."

Meanwhile, Moonbin passed away on April 19, when the idol was found dead in his apartment at 8:10 PM. Moonbin's funeral procession and burial site were not disclosed at the request of the bereaving family. Instead, Fantagio set up a memorial site for fans to visit and pay their respects.