Well unless you wanna lose gil. You might wanna break out a guide. In Zanarkand Yuna is fed up with these shoebies desecrating her memories. So at the temple she comes up with a plan. Monkeys. Well from Chapter 2 to Chapter 3 you can do this quest
Basically you need to make the monkeys mate. This is done by playing matchmaker for each monkey. This can get a little long. You first need to fina a monkey with hearts by its head. Then go around looking for the monkey with a name that matches. So a lot of backtracking a lot of memorizing or just refer to a guide and get this done.