Well... that seemed like a very contrived turn of events.
Seems awfully convenient to separate Shin together with the two new ladies. The other girl even got a "kiss" before Tiera or any of Shin's other admirers did. I have to hand it to him for giving her that mouth-to-mouth without any of the annoying fretting or fussing that newer isekai protagonists would have done.
Though it also raises my eyebrows that he had to resort to CPR when he usually has convenient magic/potions that easily resolves things like miasma, poison or near-death bleeding statuses. Why did Kanade jump into the water?
She jumped in so she could get rescued and join Shin's harem. She probably saw Shin jumping in and tried to save him not knowing he's perfectly fine fighting underwater, is my guess.
Also, he could've summoned the others along with Yuzuha like last time, but didn't. I guess to keep the ship as safe as possible.