Tantei Nana Oto Ha Akiramenai (Kadokawa Tsubasa Bunko)

[Machine Translation] I'm Nanane. I'm in elementary school, but I'm a detective. Right now, I'm considered a "sidekick" to Hibiki Shirasato, a boy detective who is relied upon by the police... But one day, people will say, "It's because you're a detective, Nanae, that we want to entrust you with our cases! I want to leave it to you! One day, I received a notice that there was a notice of a crime against the hidden treasure, Blue Sky. The person who sent the notice is the notorious and charismatic criminal "Professor"! He wants to commit a secret crime from a luxury cruise ship... We won't let you do it! !!!!! From intermediate grade.

あたしは七音。小学生だけど、探偵よ。いまは、警察に頼られる少年探偵・白里響の「オマケ」みたいに思われてるけど...いつか「探偵七音だからこそ、まかせたい!」って言われるようになるんだから!ある日、「秘宝ブルースカイへの犯行予告がきた」と連絡をうけた。予告状のぬしは―悪名高いカリスマ的な犯罪者「教授」!クルーズ中の豪華客船からの密室犯罪をやろうだなんて...そんなこと、絶対にさせないよ!!!!!小学中級から。