Norushima is the name given to a Golden Kamuy merch item that has gained its own notoreity within the fanbase. It is a "noru" style plushie of the character Tsukishima Hajime, and was debuted at the first GK exhibition. This "noru" style of plushie is remniscent of Disney's tsum tsum's, but is exclusive to characters from series published by Shueisha, whose imprints include Weekly Young Jump (where GK was serialized).
The word noru (乗る / のる) is a verb that means "to ride" or "to board"; hence, noru refers to the plushies small size and transportable shape, fitting easily in ones pocket, or pleasently in the palm of one's hand.
Norushima has gained its own fanbase and presence independent of its namesake. The love and attitude towards Tsukishima and Norushima are night and day. Tsukishima is a rugged soldier and frequently objectified; Norushima is a funny little bean, adored in a more wholesome manner. In this way, Norushima has become its own entity independent of it's namesake.
I own two norushimas of my own! I hope to add at least one more norushima to my norulitter. Out of all the GK noru plushies, norushima is the most popular and consequently, the hardest to get overseas (and the most expensive!)