If you’re talking about something like MHA those are largely made up with some influence from real naming patterns.

For what it’s worth a quick Google search will usually tell you the answer for any particular name. Just like with English, there’s a combination of:

• Names that are also real words still in use (“Sakura” or “Rose”)
• Names that are based on former vocations (“Goldstein” or “Smith”)
• Completely made up crazy shit (“L-a” pronounced “ladasha” and I wish I were making that up)
• Stuff that’s meant to remind you of something related to the character (“Otto Octavius”)
• Whatever the author felt sounded cool (“Ronan Dex”)