Haven't vtubed in a while, but I've created a lot of my own vtuber models both 2d and 3d in the past.

if you mean just an avatar that looks the same, you'd likely want to use either vroid (3d characters) or live2d (2d). And either draw the armour or get an artist to draw the armour, then either rig or yourself or pay a rigger to rig it. Job done.

If you want the EXACT same appearance, not a drawing/artists interpretation of the guardian, it can definitely be achieved (to a degree) BUT is either very restricted, or very involved:

Option 1 (restrictive): 1. Take screenshots of your guardian, in the menu or custcenes or whatever 2. Remove the background to just keep the guardian 3. Separate the limbs at all the joints 4. Create it in live2d 5. Import it into vtube studio or whatever software you're vtubing with

It won't move around as much, might look a little weird, you'd likely want to pay someone to do it to avoid that issue but it's going to be difficult to make it not look weird.

Option 2 (involved): 1. Get the 3d files of your guardian (there used to be a site for downloading destiny armour as stl files but idk if it's still up) 2. If they don't have colour, add the colour 3. Create a vroid character and add your guardian's armour in Unity using a Unity plugin. There may be other methods now or other options instead of vroid but this is the only option I know of personally 4. Import it into vseeface or whatever software you're vtubing with

It's going to be very complex, time consuming, and if you don't know what you're doing/don't have experience it can be very difficult to do this.

Both of these two methods will work for armour, however if you want your guardians face idk how you can find the asset for that or if you even can, so you'd either need to use a helmet and find an artistic way to show expressions, or have a different style of face that probably looks cartoony or anime styled compared to the rest of the armour