Nagi Sanzenin is the only heir to the Sanzenin fortune because she is the only survivor of the family besides her grandfather. She isn't just your average "rich girl". Calling her "rich" would be selling her short. The "Sanzenin fortune" is so large, throwing away 20 trillion yen in a red herring investment is considered a prank. Moreover, Nagi fell for that "prank" when she was a child - she's 13 now, and by far wiser. She doesn't particularly desire the inheritance. However, other people do want that wealth, and will acquire it by any means necessary, leading to many complications for Nagi, the least of which involve kidnappings and attempted assassinations. Hayate, her butler, is indebted to her, so Hayate always save Nagi from any accident, kidnapping, or assassination. Even though Hayate himself attempted to kidnap her for ransom money, Nagi has a crush on Hayate ever since she first met him in the kidnapping situation.
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Nagi is a short-tempered, spoiled, anti-social or socially withdrawn, hates to lose and to admit her faults, has a considerably hard time confessing her true feelings towards Hayate or anything in the fact of the matter, she acts immature a large portion of the time but is ultimately a good, educated girl. She is good at finance and likes to learn. Her mind is possessed with her own. She cares for her family and friends, but she doesn't want to show her concern directly. She usually tends to show her concern with "formal words". She is not actually a tsundere, she is more of a himedere.
Role in fanpage
Being one of the youngest tsundere girl in the fanpage, Nagi is usually isolated and not very popular on the page. Hinagiku Katsura is usually more famous than she is, but for Nagi, she doesn't really care about the popularity. She often participates in popularity voting contests,but she seldom does it for fame or attention and is merely donig it for the fun of it.