Either I missed it, or I completely forgot to add it to Takatora's history/something.
The implication is/was going to be that Takatora's father wasn't loyal to his mother while they were married. And then, of course, she died (when he was like 12), and that it's very possible that there are other Kureshima siblings out there, half-siblings to Takatora.
I put that in there/meant to put that in there as an invitation for them to be made. Takatora will welcome them into Yggdrasil gladly, if they come to him and come for their family's legacy.
He'll also see to the creation of more Zangetsu-style Sengoku Drivers, taking up Zangetsu/Melon as the symbol of the family.