The source code in "ReGLOSS '瞬間ハートビート' OFFICIAL MV" ( https://youtu.be/Ix_uXN_ybxc ) [UNOFFICIAL gist]

regloss.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace debut
{
    class Program
    {
        static void Main(string[] args)
        {
            var ReGLoss = new hololive.DEV_IS();
            hololive.DEV_IS.call(moco);
            
            ReGLoss.setMessage("Hello World!");
        }
    }
}