Icarus's only defining feature is his short, slightly curled hair.
A seemingly cheerful boy, Icarus is also brave and challenged the blackout when it appeared, where he rushed in headfirst and did all sorts of unreasonable things during the battle.
Icarus appears in Fiona's memory when Takayama Sou shares the vision he saw with Karasuma Eishi. In that memory, Icarus promised to protect Fiona from the blackouts that were plaguing the children in their orphanage. Even though he eventually succeeded, he himself was killed in the process. His death drove Fiona to awaken her Seeker abilities.