Hayato is still in Nagoya, and the three drivers from outside of Kanto are completely not used to the region’s summer heat. Commander Izumi proposes a trip to the beach, and to everyone’s surprise, their families are invited too! It’s a major familiy reunion, even with some mothers we’ve never seen, such as Shinobu and Akita’s! But Akita’s overprotective mom makes life difficult for the team when the next Giant Monstrous Being shows up. Can the team defeat the latest attempt by the Agents to cooperate without letting their moms figure out that they’re risking their lives? And just what is Commander Izumi’s motivation for moving everyone to the beach?
リフレッシュのため海水浴に行けることになったハヤトたち。ハヤトの家族だけでなくアキタ、ツラヌキ、シノブの家族もビーチに招待され、久しぶりの再会を喜ぶ。中でもアキタの母・モミジの喜びようは強烈で、四六時中アキタにべったりだ。
その時、巨大怪物体が出現！それぞれの家族に余計な心配をかけないため、ハヤトたちはフタバが提案した「スイカ割り作戦」を実行する。その作戦とは……？
出水見炎熱天氣令大家無精打采，決定帶全體人員去海灘遊玩。巨型怪物體出現，但這其實是出水的計劃，因為海邊雜訊較少，能更容易截取敵人的通訊頻率。為免讓母親們發現，眾人要分隊輪流出戰。
