Earlier quoted context omitted.
https://carnegieendowment.org/2022/08/15/south-korea-s-decap... provides this account of official ROK strategy : > Every Pyongyang district, particularly where the North Korean leadership is possibly hidden, will be completely destroyed by ballistic missiles and high-explosive shells as soon as the North shows any signs of using a nuclear weapon. For the DPRK the official strategy is not known as far as I know, but i…
Who would be "striking first" if "the North shows any signs of using a nuclear weapon"? Using a nuclear weapon would indeed be deemed an act of war. That sounds like self defense.
South Korea is explicitly aiming to striking first with the aim of entirely preventing the attack, so "any signs" should be read as "very early signs". The ROK generals are talking about striking significantly before the DPRK are clearly using a nuclear weapon, because attacking only in the case of clear use is striking in retaliation.