Miya is Missing
Near the northern bridge you'll find Grandpa standing out by the water.
He is searching for Miya, his guppy. Grandpa was taking her for a walk when
he was pushed down, tipping over Miya's bowl and knocking her into the
water. He doesn't exactly ask you to find her, but it's pretty much
implied.
Cross the bridge and then follow the riverbank north. You will come across a pond filled with tiny little fish. Use a Maggot as bait and fish away until you catch a Guppy. The fish can talk! The fish you catch turns out to be Miya, who was seperated from her "father" 10 years ago. She would like to return to Grandpa but she doesn't want to leave her friends behind. Miya asks you to catch 3 Guppies from the pond.
Bring Miya and her friends to Grandpa. He will reward you with the Panda Bobber (float D).
Rapids Battle with Naoko
Head all the way to the south west corner of the Rapids and you'll
trigger a meeting with Naoko. She wants to test your fishing skills
so she wants you to catch a Aouo at least 40 inches in size.
Just to the north where you met up with Naoko you can find the Aouo fish. You can use a Spinner lure to catch one. Bring her a fish larger than 40 inches and she'll pout and leave you alone. She doesn't give you a reward but you will need to beat her before you can continue onto the next map.
Solve the Attempted Murder
Talk to the scruffy looking man south of the Jizo save shrine and
you'll learn all about an attempted murder! Detective Yama has sent
out his police force to investigate and ask questions, but one of the
officers is blocking the entrance to the Swamp map. It'll probably
take forever for them to solve the crime so it's up to you to do it
yourself!
What you have to do is talk to the villagers in the Rapids map. When you talk to the right person you will view a cut scene between the two of you and you'll receive a clue as to where to go next. There are 8 different people you need to hunt down and talk to. When you reach the last person it turns out that the scroungy detective solved the case on his own!
The culprit gets away but the police are on the chase. Now you can get past to the Swamp map.
Feed the Fisherman
In the northeast corner of the Rapids is a fisherman dressed in blue.
He is incredibly hungry but he doesn't want to eat just anything. Hiroshi
will only eat things that he likes but he doesn't know what kind of fish
to use for his meal.
A few years ago he had a dish that was very delicious. The chef told him what it was but he didn't tell him what fish were ingredients for the dish. Hiroshi has since then been catching fish and cooking them over and over, trying to recreate the dish he ate years ago. If you can find the fish needed Hiroshi will share the recipe with you, and a special Treasure Map.
Hiroshi thinks one of the fish is a Big Iwana back in the Stream. You can find it in the Waterfall area using Fish Eggs as bait. Bring the Big Iwana back to Hiroshi but it's the wrong fish. He thinks maybe it's a Big Rainbow Trout from the Mountain region. Fish for one near Benkei's bridge using a Small Fish as bait. Return to Hiroshi and he sends you out one more time for a Big Catfish from the Swamp. Use a Buzz Bait Lure around the borders of the island in the southeast corner until you catch one. Bring it back and Hiroshi discovers that the Big Catfish is what he's been craving for.
He shares with you the recipe for Big Catfish Miso Soup and also gives you
the Treasure Map. The clue says by the downstream bridge where three
dead trees meet. There are several sets of 3-dead-tree areas in the map,
but the ones you are looking for are south of the Cooking Contest, along
the river. Examine the dirt between the 3 dead trees to find the fouth
Piece Of Something.
The Straw Millionaire, part 4
Near the waterwheel you'll find a little girl. The girl notices that you
have a very pretty item with you. The thing that has caught her eye is
the Bracelet you received in the Field. If you agree to exchange items
with her you'll receive a Pretty Stone for your Bracelet.