Kess can cast Instants in the Graveyard since you, basically, look at them as Instants or Sorceries and then see if anything lets you cast them. Normally, this is the normal rules, but Kess allows this as well.
Toshiro is different since Toshiro targets and they are never instants or sorceries to be targeted in the graveyard.
Toshiro is different since Toshiro targets and they are never instants or sorceries to be targeted in the graveyard.