For some tidbits of context
Chihaya has said in one or two streams that she adores the concept of Paras and its tragic ego-loss once it evolves (even calling that a kink?)
Since she started a Pokémon Leafgreen playtrough she wanted to go on a journey with a Paras and eventually caught two of them. One she named Promise and one she named Friend.
Trough out the game she trained both Paras never evolving them, always cancelling with B on the evolution screen.
But at the end of the Elite 4 and the Champions battle, she declared the journey was over and let Promise evolve into Parasect and fulfilling that tragedy she had set out for... basically her idea was to carry her over the finish line all the way