Kinemon has proclaimed that 5 people have comeback in time. Momonosuke, Kin’emon, Kanjuro, Raizo, and Kiku make 5. Who is the mysterious figure highlighted in green?

This guy was with them right before the time travelling but after arriving 20 years later, he (or she) wasn’t around. Funny thing is how Kin’emon and the others ain’t telling Luffy about this or perhaps the next chapter will tackle about this.

Possibly, this guy was the one who was tasked to protect Momonosuke’s little sister, Hyori.

So there are 2 possibilities:

1-Hyori and the mysterious guy didn’t join the group to travel to the future so they were constantly hiding until now and have changed their identities.

2- They were sent to another time much further (or earlier) than Momonosuke’s group.

Finally, I want you all to remember the mysterious character in Chapter 631 cover page. This cover page shows Crocus and Laboon for the first time after the timeskip. Crocus is drinking with an unknown person wearing a Samurai or Japanese clothes which it seems related to Wano Kingdom.

I highly suspect that this is the same guy we are talking about. Look at that strawhat! Look at that design!!!!

Could this be him shown in this cover? What do you guys think?

*Theory by JomaBusa