I'll be going to Japan in the next few months under an student exchange program, I wanted to get a multiple-entry visa but the lady at the embassy did not ask (my fault for not checking) so I just assumed everything went swimmingly. I had plans to visit nearby countries other than Japan but with what I have right now I won't be able to. Anyone here has any experience on this? Like is it possible to change to a multiple-entry from a single-entry? If not, can I reapply immediately or do I need to wait a specific time period? Thanks..

Ah yes, thank you for the information. I've reached out to my nearest consulate office and they assured me that I will receive a residence card which can serve as a multiple-entry permit.