Umm the main episode you need to watch for Ai-chan is the episode where she comes:
129: The Girl From The Black Organization and The Murder of the University Professor
(2 hour special)
Black Organisation:
001 Roller Coaster Murder Case
128 The Black Organization 1 Billion Yen Robbery Case
129 The Girl from the Black Organization and the University Professor Murder Case
176 Meeting With the Black Organization Again (Haibara)
177 Meeting With the Black Organization Again (Conan)
178 Meeting With the Black Organization Again (Resolution)
309 Contact With the Black Organization: Negotiation Chapter
310 Contact With the Black Organization: Pursuit Chapter
311 Contact With the Black Organization: Desperation Chapter
345 part 1 Head-to-Head Match With the Black Organization; Two Mysteries of the Night of the Full Moon
345 part 2 Head-to-Head Match With the Black Organization; Two Mysteries of the Night of the Full Moon
425 Black Impact! The Moment the Black Organization Reaches Out!
462 Shadow of the Black Organization: The Young Witness
463 Shadow od the Black Organization: The Strange Illumination
464 Shadow of the Black Organization: The Mystery of the Big Reward
465 Shadow of the Black Organization: The Pearl Shining Star
You can also find episodes with individual members of Black organisation on this website:
link
They have lots of useful info and also complete lists of what episodes characters appear in. :)
