Reimu drugged Alice here (that's a sake box in the third panel), so she could come over and take care of her. At the end, Reimu gave Alice one of the pills, basically saying "your turn".
Reimu drugged Alice here (that's a sake box in the third panel), so she could come over and take care of her. At the end, Reimu gave Alice one of the pills, basically saying "your turn".
With how cagey Reimu is with her answer here, along with Alice's observations, it's probably because Reimu likes her, and was planning to confess as much. Given Alice's overall reaction, the ploy confirmed the feelings are reciprocated to some degree, which is probably why Reimu gave her the pill in return - to 'level the playing field' as it were.
(...not that I think that makes it okay, mind. But I don't think we're really supposed to consider the ethics of mildly poisoning someone you love in order to prove you can take care of them.)