Sari is a strange one among the champions since her core works a little differently. Luke and Nyx are very internally power because their cores connect solely to their inner emotions. Delvin and Timoran have cores that connect to how they act toward others as you’ll see when their turn comes. Sari actually falls into both categories, which makes her an interesting bridge character. This fits in a lot with a belief that she is the heart of the champions and her presence keeps them on their original paths. I still haven’t figured that part out yet even though it does seem that Sari tries to keep everything light and positive when things go dark.
Sari’s core is love and it isn’t as simple as you may think. This can best be explained in the Kira/Luke/Sari triangle that has reached an interesting point in The Compass Key and an even more interesting point the later books. Anyway, she gets power from being loved and making others feel loved. It isn’t only about her, so she actually gains strength from helping Luke and Kira in their relationship. Her causing trouble is a sticky subject because while she gets weakened by her role in the confusion, she is also empowered by the love she feels from Luke. This actually evens out, so neither gains nor loses prowess. This means it is rather difficult to hurt her core without emotionally ripping Sari a new one in every direction. Though there is something within The Compass Key that comes close and it probably isn’t what you think.
Now this isn’t solely about romantic love. Sari’s friendships empower her especially with Nyx. The teasing and playful antics strengthen the bond between them as well as make the typically uptight caster a little more relaxed. Nyx’s fierce protectiveness of Sari is another thing that adds to this ‘love core’. One could even say that the relationship with Nyx is where Sari gets the majority of her power. There are connections to Fizzle, Timoran, and Delvin, but Nyx is certainly the strongest relationship.
I have to admit that Sari’s core means there is a focus on her subplots and emotional interactions. The other characters are certainly more action-based than her, but she brings a fun dynamic that gives me a break from the main plot. It isn’t difficult to have her start a conversation up with a fellow champion about some relationship issue because she has an instinctive interest in such things. One could say she gets a little energy from the love people share in her presence. Maybe this is why she’s being considered the ‘core’ of the champions.