You can do this at the start of Chapter 7
You can only do this at Noon
Go here and Ryoma hears a guy telling another guy that he's heard there's a "Black Ship" near here.
Leave the area and then return to this area Ryoma sees a crowd of people. They see a black ship with a foreigner aboard and think he's come here to kill them all. Ryoma asks the man who he is, but he collapses to the ground, saying he's seasick. Ryoma wonders what could cure him of his seasickness and says he should ask around.
Talk to the onlooker near this area and he tells Ryoma he's heard a good way to get rid of seasickness is drinking.
Talk to the foreigner again and choose the TOP OPTION to take him for a drink.
Sadly, that didn't rid him of his seasickness, so Ryoma says he should ask around again for more ideas.
Talk to the onlooker here and she tells Ryoma she's heard exercise is a good way to get rid of seasickness.
Talk to the foreigner again and choose the TOP OPTION to give him training. You now fight the foreigner at the dojo.
Sadly, that didn't help him either, so Ryoma says he should ask around again.
Talk to the onlooker here and he tells Ryoma he's heard eating dried plums helps with seasickness. If you don't have a Dried Plum in your inventory, you can buy one from location 4 on the map above - Ichikuraya.
When you have a Dried Plum, go back to the foreigner and choose the TOP OPTION to give him the plum.
This worked and he is now rid of his seasickness! He thanks Ryoma for his help, then Ryoma asks why he came here in the first place. He says he came here to open up the country to the west for foreign trade. He introduces himself to Ryoma as "Mushu Pony" (not sure why they didn't just use the name "Matthew Perry", since that's who this guy is supposed to be - he even looks exactly like the real Matthew Perry). He says the first thing he wants to bring back over to the west is Dried Plums, saying they don't have anything like that where he's from! Ryoma shows him where he can buy them from, then Pony thanks him, but then some guys show up to confront him. They are more guys who hate foreigners and want them away from the country. A fight against them begins.
After the fight, Pony gives Ryoma a Precision Machine, then heads off on his boat. You are also rewarded with 350 Dharma.