This is what I've found:

Garen: Broken Glass *Broken promises or shattered expectations. * Your feelings may be hurt or a situation may be turning into a crisis. * Interesting Note: Shattered glass symbolizes the fragility of our relationships and reminds us that we must treat our relationships with extra special care. It teaches us that in times of joy we must also realize life also brings sadness and sorrow.

Like many other people have been pointing out, I guess the situation with Garen is his loyalty for Demacia and contrasting love for Katarina. Maybe he broke "promises" to the Demacian army by seeing Katarina, or his "expectations" of being in the army were far more gruesome than he imagined? The "crisis" could be the ongoing conflicts between Demacia and Noxus, which in turn, threaten his relationships between his allies and his lover.

Sona: White Butterflies * Symbolizes the souls of the departed ones.

Maybe this has to do with the countless Ionian lives that were lost to Noxus forces because Sona allied herself with Demacia at the time. It could also represent the loss of her foster mother, but the number of butterflies flying by must represent more than just one person... maybe.

Vi: Ashes and Smoke (?) * Have to do more research on this one?

Zed: (Cherry) Blossom Petals (?) * I'm not sure if they are cherry blossoms, but if they are, there's a lot of interesting meanings behind them. * The blooming period of cherry blossoms are short, leading to an instantaneous flourish and sudden death. In Japanese culture, the flower serves as a reminder of mortality and humanity knowing that the life of a human being can end anytime just like the flower. The cherry blossom exemplifies this human condition, making people realize that life is short and that they should live it well.

Could be a reference to the death of Zed's Master/Shen's Father.