How is Botan (the Japanese rice candy) made?
Do you mean this one?botan rice candy. 

If so, in Japan it is actually known as Bontan Ame  (meaning pomelo candy) as shown in this description.

Here is a link to how a similar milk version is made (I think you would use mandarin/pomelo (bontan) juice in there somewhere for what you want), but it is in Japanese...Perhaps the pictures will help but...sorry, I don't know if it's ok to translate this...but it says: milk 500ml, sweet glutinous rice 500g, sugar 500g, mizuame (maltose; could use corn syrup instead) 600g, potato starch 200g, and a tray 31cmx24cmx3.5cm. Briefly, it says to soak the rice for half a day, then drain, and blend with the milk for 2-3 mins. Transfer to a pot and simmer on medium heat for 20-30 mins. Add sugar in a few lots, mix until dissolved. Drop to low heat, add mizuame and stir/knead very well - the firmness of the final candy will depend on how long you do this. Dredge tray with a thick layer of potato starch then pour the mixture in. To harden, refrigerate when cool.