These little guys look exactly the same as Kodama's, the only difference is their color as they have a purple hue around them.
For this trophy you need to approach the Sudama and speak with them, then you need to drop an item. This can be any item however it is recommended to drop any soul cores you may have as a chance to get the Kodama core.
Once the Sudama exchanges the dropped item they will disappear and the trophy will pop.