Board Thread:General Discussion/@comment-11016223-20130904052318/@comment-14250-20131017074656

I see this thread as spawned by a straw-man argument. I don't think anyone literally thinks the two to be biologically related.

However, there are biological relations and emotional familial relations. Though currently estranged, if Karai is ever considered Splinter's daughter, much like the Turtles are considered his sons, this would create an emotional familial relation between the two.

In the same sense that it would be weird if Karai dated Shredder in the 2012 universe (they're not biologically related, but he raised her and there are emotional relations here), it'd also be weird if Karai dated Leo. Not so much now since neither are aware of anything, of course, but as viewers, it's possible to foresee complications beyond that which Don and April might experience.

Of course, April might be seen as Splinter's new adopted daughter, though not to the same degree as Karai and Shredder or Splinter and the Turtles, due to the difference in duration of companionship.