Upset is the opposite of Happy. Happy is related to Very. Very is related to Seed. 
Mere is a synonym of Simple. Simple is related to Plain. Plain is related to Special. 
Upset <--Antonym--> Happy <--RelatedTo--> Very <--RelatedTo--> Seed 
Mere <--Synonym--> Simple <--RelatedTo--> Plain <--RelatedTo--> Special 