The title is wrong.
The issue is not that the character is invicible (can't be killed), but it appears to be invisible.
In any start of layout event, just create an object "main_char" to resolve the issue. Always remember instances get destroyed when passing from a layout to another, except if their "global" property is set to "Yes"
(which in your case is maybe not what you want either or the main character would appear on the global_map layout too, the title didn't mention it...)
Tips for posting when asking for help.