>>715743343
I mean due to the nature of Gacha Stories never ending (until EOS) it's unlikely they'll ever have a canon wife/husband for Belle or Wise since they'll always be adding new Agents to the roster. But since your Sibling is another MC they'll always remain relevant or at least close too the plot.
If anything that privilege makes Belle MORE canon than typical 'for you' characters like Astra, or Vivian.