I'm pretty sure they rotoscoped that waving animation. Rotoscoping has a bad reputation, but it doesn't always have to look horrible. If it is done with certain care rather than just lazily coloring live video footage it can actually yield amazing results, Bocchi is a good example of this.

Although this show is fictional, almost all the causes in this show are actually true. They don't say specific names of the substance most of the time to protect viewers from using it to harm anyone intentionally in real life, I guess. In ancient time, some of the white face powders contained lead or mercury. And some plants/trees such as Nerium oleander is poisonous when burned. This show may be a bit difficult because of not only the genre but also the time and place this show is set (like, ancient China). You don't hear those words like eunuch, concubine, or courtesan etc. everyday in real life. lol But I would be so happy if you like this show!