霞雲の海 is built by grafting a real Japanese scenic term onto Mist Breathing's vocabulary. 雲海 (unkai, "sea of clouds") is an actual word — it's what you call the view from a mountain summit above a cloud layer, a famous phenomenon at sites like Mt. Fuji and the Unkai Terrace in Hokkaido. Gotouge doesn't use 雲海 directly; instead the compound is reordered and thickened into 霞雲の海, "sea of haze-cloud," which keeps the recognizable shape of the existing word (X-no-umi, "sea of X") while making the substance itself denser and more oppressive than a scenic cloud layer glimpsed from a mountaintop — appropriate for a technique meant to blind and disorient an opponent at ground level rather than to be admired from above.
The corpus's automated English alignment misattributes this occurrence badly, and it's worth spelling out exactly how. The pipeline's stored text for this page reads "EIGHT-LAYERED MIST!!" — which is Form Two's name, not Form Five's — a page-offset artifact from the same stretch of Vol. 19 that misaligns several consecutive pages during this fight. The real VIZ line, confirmed by direct visual check on the following page of the tankōbon, is "SEA OF CLOUDS AND HAZE! / MIST BREATHING / FIFTH FORM:" — a clean, correctly-numbered caption with no relation to the corpus's stored guess. This is a useful cautionary case: a byte-exact citation against unverified OCR would have shipped a factually wrong VIZ quote under a confident-looking source reference, which is exactly the failure mode visual verification exists to catch.
Dramatically, this is the form that draws a reaction out of Muzan himself — immediately after seeing it, he says (in the Japanese) roughly "Mist, is it... I see... not bad," the closest thing to a compliment Muzan pays anyone in the series before turning hostile. Pairing Sea of Clouds and Haze right after Eight-Layered Mist in the same combo suggests these two forms are meant to be read as an escalating pair — first many layers, then an entire flooding expanse — before Muichiro shifts to the precision of Shifting Flow Slash and finally to Oboro, his own invented seventh form.