Ilonka is the main lens through which we view most of the season. She starts "The Midnight Club" as her school salutatorian on the cusp of graduation. Then she discovers she has cancer, and slowly watches as the high school life she knew — along with all its friendships and crushes and disappointments — fades away.
It's a harsh introduction to a pretty harsh show, and one that tells us the stakes early; each of the characters we're about to meet and fall in love with has a terminal illness, and therefore may very well die in the foreseeable future.
The main mystery plots — what happened to Julia Jayne, the whereabouts of Athena and Aceso, the ritual of the Five Sisters, and whether Dr. Stanton is hiding anything — are all centered around Ilonka because she is the clubber most stubbornly addicted to the idea of spontaneous recovery. After all, it's the story of Julia Jayne that attracts her to Brightcliffe in the first place.
In the end, Ilonka narrowly escapes death by following her instincts and intuition, which serve her well throughout the story. While her journey doesn't necessarily feel complete, it does end on a high note. As Kevin says, her stubbornness about finding a cure is just part of what makes her such a potent symbol of hope.
