Zeku’s theme nusic incorporates Strider’s theme music.

If you listen close when Old Zeku is doing his slash kicks, they used the same
sound effect used for Strider’s sword slash in the Marvel games.

That kick move even shares the same name as Strider’s sword slash.

Old Zeku’s move set reflects Strider a lot actually, just without the weapons. And even though Young Zeku’s moves are based on Guy, Young Zeku’s costumes are basically Strider costumes. Zeku’s Battle Costume isn’t even basically Strider’s costume. It just IS Strider’s costume. Look at this shit:

https://pbs.twimg.com/media/DMOyMweUQAA0OHn?format=jpg&name=large

https://pbs.twimg.com/media/DMOyE81UMAEaCJm?format=jpg&name=large

And Zeku’s Critical Art is also just Strider’s level 3 hyper combo from Marvel mashed up with one of Guy’s ultra combos from SF4.

I don’t know what kind of magic mumbo jumbo Zeku uses to turn young again, but Strider is supposed to be set in the future. When Guy took over his ninja clan from Zeku the story goes Zeku went off to start a new school of ninjitsu. With all the hints Capcom is dropping I think it’s safe to guess that new school goes on to become the Striders in the future.