The Invasion of Uminari Island is chapter 19 of the Hinowa ga Yuku! manga.
On a certain day, Soukai King Sotetsu is enjoying the view of the sea while Hisame answers his question with the blunt and honest tone, surprising both Maruge and Sotetsu but the King likes his honest answer. He plans to get rid of the pirates on Uminari island that cause disturbing actions on trading vessels.
Waniba comment that the pirates may build a small hideout, rather than a base of operations based on danger beasts that naturally dwell on that island. When Sotetsu ask what Hisame may think of, the answer once again surprises Maruge enough to persuade him to not take the request at face value. Hisame proposes an attack with small forces rather than a big one since the pirates can make money from hostages. Seeing the fervor eyes of Hisame, Sotetsu asks Shion's opinion while he commends that people from Yaenami village are very skilled and he gave the clearance for Hisame to go on the mission. Waniba met with Rinzu before Soukai went to subjugate the pirates. He notices her perfume was changed but his face turns into jealously upon seeing Hisame and Rinzu are chatting casually.
Departuring to the ocean, Hinata gave a speech to her units to boost their morale. She, unlike Hisame, will not rush herself to aim for Commander title as she wants to complete one mission at a time. Meanwhile, Saiha was training and she was informed of incoming Soukai Navy to engage her. Kumehachi spots the enemy pirates and Suzumaru advise Hisame to engage them with arrows in order to not raise any suspicion amongst the pirates. The pirates thought that they were panicking but upon boarding Hinata's ship, what he saw is his men were being slaughtered by Hinata's unit. After a couple of skirmishes, Hinata's unit starts to get their confidence but they were reminded not to get overconfident.
Meanwhile, the pirates on the ship wondering how are the boarding parties doing but Hinata suddenly ambush and defeating them. Before Hinata can seize it, she felt something is approaching and dodge Saiha's attack. Diving to the ocean, Hinata faces Saiha at one on one duel.