It's time for another Parasite Monster Girl! Meet Ophelia the Ophiocordyceps Monster Girl.
Ophelia is based on the Ophiocordyceps genus - the diverse group of parasitic fungi better known collectively to most people as the "zombie ant fungus". But what most people probably don't know or appreciate about Ophiocordyceps is that there isn't just a zombie ant fungus (the most well-known species is O. unilateralis), but there are multiple species of them, all infecting different species of ants. And it is not just ants that they infect, there are also many, many other species that infect a wide range of different insects, and they all do the same zombifying trick to their hosts as the ant-infecting species.
In-universe, Ophelia is an Emissary Ascocarp - a physical avatar of the Hyphal Mind. Also know as the Speaker to Animals, Ophelia is in fact a special type of fruiting body that the Hyphal Mind produces to communicate with any foreign sapient animals who wander into Myceliated Forests. The Hyphal Mind produces specialised spores that infect one of the many boar-size monster ants that are commonly found in the Myceliated Forest to produce this physical manisfestion of the Mind. The role of Ophelia is to explain the Contract that one unavoidably enters into with the Hyphal Mind by merely setting foot into a Myceliated Forest, and whether the visitor has been deemed by the Hyphal Mind to be a potential Partner or Substrate (most animals are consider in a sub-category known as "Mobile Substrate").
Design note: Some of you might recognise that this is a total re-boot of a character that I drew almost two years ago - Ophelia the Cordyceps Fungus Monster Girl - so this is a complete redesign of that character that is morely closely based on the morphological features and colour scheme of Ophicordyceps fungi. This ended up giving this new version of Ophelia a very autumnal feel - seredipitously, this actually matched the season where I am, as autumn has just begun....
A Partner means you get to stay alive (to serve the purpose that the Hyphal Mind has assigned you with), but part of the Hyphal Mind will continue to dwell within you until you can no longer fulfil your obligations - at which point you will be considered as Substrate and treated as such.
Substrates are digested.
With a few exceptions, animals are rarely considered as Partners, and even then only as temporary Partners that can become Substrate at any moment, should that be required by the Hyphal Mind.