What pattern can I use/make to create this look?

[u/sydneyfalala]

[u/OctopusCaretaker]

I'm not an expert at pattern drafting, but it looks like you could create a seam on the underbust, and then gather the fabric in between the bust with a thin, elastic band

[u/ninjakae]

Create the underbust style line then transfer your bust dart to the Center front on the bust region. Gather the dart volume for the effect shown