How would Tormanu feel about empowering weak creatures purely for the sake of making them worthy challenges?
Tormanu doesn't really choose who they strengthen with their magic. They simply sing, and the harmonious chorus can he heard for hundreds of miles. The magical aura of this music is so strong that the elements themselves fall into its rhythm, the wind and waves keep time with the beat, and even geysers and other geothermal activities that have been dormant for ages will swell at the crescendo of a verse.
Within the sound of the music, wild plants and animals will grow in strength, vitality, and fertility in relation to how close they are to the source of the sound. Anything domesticated or tamed will gradually become wild again under the music's influence, growing stronger as they become wilder.
Tomanu gives virtually no thought to whether something is weak or strong, because compared to them, everything is weak. The concept of a "worthy opponent" is a totally foreign concept to them because they haven't encountered anything that could challenge since they gained their emergent intelligence and ignited their spark eons ago.
They have seven immense hearts and their hide is thicker than most swords are long. Their strength is measured on a seismic scale. Their jaws have a bite force comparable to the sheering of tectonic plates.
Each of their necks is approximately the same length and width of a full-grown redwood tree. And trying to cut off one of their heads would be about as difficult as chopping down a redwood in a single chop (before it snaps you up with dozens of obsidian-sharp teeth.) And even if you managed to succeed at cutting off one head, it would just fully grow back within a decade anyway.
For all these reasons, and more, the only real threat to Tormanu is fighting and discord between their own heads.
Narratively, this means that Tormanu is not very useful as a protagonist or central character in a story, but they can be great as a side character or force of nature. (Either to serve as a help to the protagonist, a challenge to get in the way, or even just a feature of the landscape to avoid.)
With that in mind, if anybody ever wants to include Tormanu in a story you're writing about your own fanwalkers, please feel free to do so! (Just as long as your story doesn't have Tormanu dying, speaking in words, or doing anything malicious or evil.)