If you ask me, I could see Karai and April having a sisterly relationship; especially after Karai found out the truth. It probably would have happened if Karai hadn't mutated so early.
(I was dumbfounded when that took place. Poor Master Splinter)
Based on little experience in Japanese culture, April could be considered as a little sister to Karai (though they're the same age). Earlier in the show, in "Karai's Vendetta," April repeats Karai's prayer over the food to show proper manners, I guess. With both being "related" to Splinter and all (Screw Karai's mutation) they could have become good friends.
It's almost like a slightly twisted Japanese version of "Frozen".
I was comparing Frozen's Elsa and Anna to Karai and April. Somehow I saw the resemblance.
I had to search those Japanese outfits on Google to be sure I was drawing them right; and I was trippin' over trying to find to right color for Karai's skin tone
Her color has a lot of yellow, but it's also faded, it took a minute.
All done in MS Paint!
April and Karai/Miwa (c) nickelodeon/MirageStudios
Artwork is by me