|This article is about a/an ally in Kamen Rider Decade.|
|Series:||Kamen Rider Decade|
|Homeworld:||Earth (World of Negatives)|
|First Appearance:||The Nega-World's Dark Riders|
|Last Appearance:||The Walking All-Rider Album|
|Number of Episode|
Full list of appearances
The World of Negatives' Natsumi (ネガの世界の夏海 Nega no Sekai no Natsumi) is the World of Negatives counterpart of the real Natsumi Hikari and one of the few remaining humans in the World of Negatives. She confronts her counterpart in an attempt to warn her of Otoya's scheme, only to be forced to dig up the K-Touch she had hidden. She eventually gives her goodbyes to Natsumi while entrusting the K-Touch to Tsukasa, remaining in her world out of hope for the future.