So Jupystar is pronounced like Jupistar.
Jupis, like lupis.
People try to be too clever with these portmanteaus, and end up with either something unfortunate or unpronouncable.
That's what I said. But differs to what you said before. /Jupi/ has only one stress; your previously mentioned pronunciation requires two, also two s rather one that exists in the word.
So Jupystar is pronounced like Jupistar.
Jupis, like lupis.
People try to be too clever with these portmanteaus, and end up with either something unfortunate or unpronouncable.