Big Duel at the Southern Sea! (南海の大決闘！, Nankai no dai kettō!) is the 47th episode of the Inazuma Eleven series.
On a cruise to Okinawa, after receiving the news of the flame striker, Endou's positive that the flame striker is definitely Gouenji, with Coach Hitomiko going ahead before them to Okinawa to search and find out the truth herself. A few of the team members have second thoughts about the flame striker being Gouenji, saying that it's best to actually know it rather than think it.
Megane then starts to admire the coral underwater while on cruise, and with warnings from Kabeyama about leaning too close and falling over, Megane literally falls off the boat, and slowly sinks into the sea. A surfer then comes to his rescue, and drags Megane to shore, making the whole team stop at Agatou island, and miss the next boat trip to Okinawa, forcing them to stay the night at the Island. Endou takes this opportunity to practice for the next match against Aliea Gakuen, and Touko takes the practice as an opportunity to learn a new hissatsu in order to become stronger. Endou attempts to do Seigi no Tekken though he fails at doing so, wondering what the 'whirl' meant. Tsunami then suddenly interrupts the practice by jumping in from the sky, asking whether soccer was something you could do on the beach, then going off with his surfboard to relax.
The practice goes on as usual, and Touko attempts a shot, only to have it stopped by Tachimukai's Majin The Hand, then deciding to do Butterfly Dream with Rika. Rika starts to protest, saying that she should be doing it with darling instead, though Ichinose then states that it would better if Rika and Touko did it together. This changes Rika's attitude to doing the hissatsu with Touko, making Rika become high-spirited towards doing the hissatsu. They both attempt the hissatsu, though Touko kicks it too fast, making it fly over to Tsunami's surfboard, making the surfboard land flat on Tsunami's face. Tsunami asks who did so, and seems to get angry though instead he thanks Touko for waking him up so he wouldn't miss the 'good waves'. Rika looks back and forth at Tsunami and Touko, then having thoughts of some chemistry going on between them.
At Aliea Gakuen, Gran and two other people, one under a blue light and another under a red light. They comment about Endou Mamoru, with Gran calling him 'a fascinating person'. The other two people comment that each of their teams, Prominence and Diamond Dust will steal the title of the Genesis.
Back at the practice, Rika and Touko try Butterfly Dream again, though it failed again, swerving the ball straight at where Tsunami is surfing, making him kick it back with intense power at Tachimukai. Tsunami comes back down to them saying that the ball coming at him was a surprise. Endou asks him whether Tsunami has played soccer before, where Tsunami comments that he hasn't. And after Kidou talks him Tsunami into playing, Tsunami begins to practice with the team, doing increasingly well on defense. In one part of the play, Touko and Rika manage to successfully do Butterfly Dream, and Tsunami creates his own hissatsu, Tsunami Boost.
Later in the evening, Tsunami goes over to visit Raimon, bringing them fresh seafood for their dinner. They begin to chat, and Tsunami then reveals that he is a 9th grader (in other words, 15 years old), making Endou apologize for the freelance talking. Tsunami comments its no big deal, then introducing himself to the others properly.
The next day, Raimon leaves on the boat to Okinawa, with Tsunami waving them off, thinking about soccer.
[Endou Mamoru] As long as we've got motivation, we can make a field anywhere!