Absolutely do not ask artists if you can have their characters and treat them as your own, particularly if you don’t intend to pay them in any way.
You know, if this situation were different and someone was asking Disney for the rights of one of their characters without paying a single dime, the company as a whole would just laugh at that person and turn them down. Since that’s not how it works for major companies, why would people think that’s how it works for independent creators?