Similar is a synonym of Twin. Twin is a type of Sibling. Brother is a type of Sibling. 
Shock is related to Unexpected. Unexpected is a synonym of Casual. Casual is the opposite of Inevitable. 
Similar <--Synonym--> Twin --IsA--> Sibling <--IsA-- Brother 
Shock <--RelatedTo--> Unexpected <--Synonym--> Casual <--Antonym--> Inevitable 