The appearance of snowflake sand on the surface has sent Shioshishio into a panic, calling all and sundry back to their homes including the children from their school life on dry land.
Uroko is quick to explain what's going on to Hikari upon his return to the ocean - in short, a tale of years gone by prophesies that the advent of saltflake snow falling is the precursor to an ice age of sorts on the surface, caused by dwindling support for the Sea God on this occasion. For the people of Shioshishio, the answer to this crisis is simply to hibernate and sleep until the cold spell dissipates, but the same can't be said of those living on the surface, who will surely perish.
Naturally, Hikari initially refuses to believe or accept this, and then switches his focus to instead pondering how those on the surface can be saved. The obvious answer is to fully reinstate the Ofunehiki celebrations, but can he really persuade everyone to assist with this, especially as the suggestion seems to be that this ice age is still some way away from wiping out life on the surface? In the midst of all this, feelings are inevitably charged all around, no more so than in Manaka's case as she tries to wrap her head around her feelings for both Hikari and Tsumugu, while things are also moving in an interesting direction for Chisaki and Kaname.
As per last week's episode, Nagi no Asukara is still proving accomplished and balancing its big picture (and some nigh-on apocalyptic conceits) with the small but important matters of the heart amongst the cast. Perhaps its vague allusions to religion and global warming within its concept of a forthcoming ice age feel a little forced, but they're never pushed too hard into what continues to be an interesting story on both of the levels that it seeks to represent, courtesy of a scenario that melds the two together very well indeed.