Oh man, this is amazing. I love it! All the references to a certain Capcom series, from the musical-themed robot sibling names to the older sibling to 'I cannot defeat Wind Knight', and more - and then all with the absolutely lovely queer themes and the two siblings never feeling quite comfortable in their assigned roles and being better at the ones that they chose - temporarily, they assure you! - along with what happened with the elder sibling instead of the dangerous power source...
I cannot wait to see more, to see the scenes you allude to in the summaries and to watch Allegro and Sonata settle into the roles they choose - and hopefully find acceptance from the rest of their little family, once they realise they truly do fit in each other's assigned roles, as they never did in those assigned to them. And hopefully they can even heal the damage done to their family before they were born, bring their father to acceptance and understanding and their sibling back home.
Also I have to say, I loved how after the siblings switched, you referred to them in gender-neutral terms until they picked their new names and settled into their true selves, where you gave them the dignity of their chosen genders!
Eagerly looking forward to more on this project!