Epson Y465ss127mo - Manual (Page 138)

Keep in mind that user-defined characters are stored in RAM, which is
not permanent. Whenever the printer power is turned off or the printer is
initialized with the INIT signal, the user-defined characters are lost.
(Some computers do this each time BASIC is loaded.) ESC @, however,
does not destroy user-defined characters.
Using Software and Graphics 4-33