neptune.

(All examples used are direct quotes from Arashi, they are romanised for ease of reading)

In Joseigo (also sometimes referred to as onna kotoba 女言葉, literally; woman words), different particles are used at the end of a sentence to soften it. Some common ones are, wa, wa yo, wa ne, da wa, no, or opting more often for the polite invitational mashou.

Kyou wa nakanaka haado na ichinichi datta wa ne.

Saikin, oishii ranchi wo dasu omise wo mizuketa no.

Ufufu, sou na na yo~! Ureshii wa, Ritsu-chan. Kizuitekureta no ne ♪

"No" in particular is often a more feminine grammatical replacement for -ndesu or -nda or -nandesu which go on the end of sentences. Attaching this grammar element to the end of nouns or the short form of verbs can indicate there being an implicit reason or explanation for something. The second example used above follows a sentence that is an invitation to eat together, the "no" indicates that the sentence is an implicit explanation for the question that came before, mentioning she recently discovered a new shop. This can also be seen with the recognisable na no that's typically used on the tail end of nouns and na adjectives, among others.

Another very common ending element that comes up in Arashi's speech is the well known kashira, which is often seen used as a replacement for kana. Used for wondering and questioning.

Tama ni wa issho ni ohiru demo dou kashira?

You will also notice in this example the use of o + noun, adding o or go to the front of certain nouns makes them more polite, which is also used in Joseigo, likely borrowed from Japanese polite language, particularly Sonkeigo. Joseigo sometimes presents a unique approach to language in that way by combining casual and polite elements in sentences.

In more neutral or masculine language, nai + ka can be used to indicate an invitation or prompting intention to perform an action, a more casual form of the verb conjugation -masenka. Similar to English's "won't you do-" or "don't you want to- or "why don't you-" in how it adapts an otherwise negative conjugation into a positive question. However Joseigo often omits the final ka, making the question implicit to the sentence's intonation. This sort of questioning is also considered somewhat more polite because it does not give direct commands, but rather reframes intention in the form of a question, that makes it less direct and potentially aggressive or too forward. When not used with words that can conjugate into nai forms, janai is used instead.

Yokattara, tameshiteminai?

A final side note is that the first pronoun atashi is also heavily associated with Joseigo as the intention of the dialect is to communicate a feminine and softened edge, which atashi achieves. It's also a much more casual pronoun, especially when compared to similar pronoun watashi which is considered more polite to use.

I don't have much more to mention, it's hard to expand beyond "this is how it works and Arashi uses it" but gendered language in Japanese is very interesting, there are also more masculine speaking styles. I find this side of Arashi's speaking is really important to how she is communicated as a character, providing a brighter and cuter charm to normal language that aligns well with her personality. Arashi is already very expressive and I find her Joseigo is a part of it, bringing a flair of individuality to her language that accompanies her cheerful demeanor. It's a shame that English doesn't have a straight forward equivalent to it, much of it is lost in my work. I hope in the future more people will be able to recognize her Joseigo and appreciate the extra sparkle it brings to her.