Ai Haibara and Mitsuhiko Tsuburaya
From Detective Conan Wiki
Relationship analysis
Mitsuhiko develops heavy romantic feelings for Ai, and Ai is aware of this. Ai uses his feelings to her advantage when she needs him to do something, but she also does admire his courage during missions the Detective Boys must perform and respects his feelings. Ai hasn't shown any romantic feelings for him, but she slightly admires his knowledge. Haibara seems to like tempting Mitsuhiko for making fun of him. She also in some episodes showed more confidence with Mitsuhiko than with Ayumi or Genta. Their "love" could be called "puppy love". This pairing has a deep connection with Ayumi and Conan relationship.