TIL Honoka is a war criminal.
Well, AKSHUALLY, the rules of war do not apply to irregular forces, i.e. any unlawful combatant, meaning those who are not from state forces or a militia. This is because partisans, insurgents, rebels, members of a Freischar, etc. do not act under the authority of any warring parties (and treating them as such anyway would open many perverse incentives). Whilst it is unclear how µ's is organized here, they likely can be treated as a PMC. And whilst the legal status of mercenaries is something people write their dissertations on, i doubt Ms. Kosaka could be charged with war crimes.
You could however try to charge her with crimes against humanity in the Hague, as Japan is a member of the ICC. Now, arguing that noodlekind enjoys human rights is tenuous at best, but the Rin-chan ramen might qualify as important cultural property or even important cultural property under special protection. This again would be a trivial charge under the Geneva Conventions (which explicitly recognize Pax Cultura), but in her case (being tasked by Japanese officials to engage the ramen) it is more likely one of them will be prosecuted (with possible sentencing) instead of her.
TL;DR:
Against her best efforts, Honoka is not a war criminal. This is mostly a failure of international treaties though.