Major manga and anime properties are protected by multiple overlapping legal regimes, not by copyright alone. Character names, character designs, logos, and series titles are typically registered as trademarks in addition to being protected by copyright. The layering is the principal reason a property's commercial control can survive long after the underlying work has been published.
What copyright covers
Copyright protects a specific creative expression: the manga chapters as drawn, the anime episodes as produced, the script as written. Copyright does not protect names, titles, or single-word labels — these are too short to qualify as creative expression in most copyright systems. Copyright protection is automatic and lasts for the author's life plus 70 years (Japan, since 2018), but expires eventually.
What trademark covers
Trademark protects words, logos, character names, and other source-identifiers when registered for specific categories of commerce. Trademark protection requires registration and is jurisdiction-specific, but can be renewed indefinitely. As long as Bandai Namco continues to register and renew 'Gundam' as a trademark in the toy, video-game, and entertainment categories in each jurisdiction where it sells products, no other company can use the name 'Gundam' on competing products even after the underlying copyrights have lapsed.
The practical effect
Layered IP protection means that the long-term commercial value of a property is preserved through trademark even after copyright expires. Astro Boy's 1952 manga chapters are approaching copyright expiration in some jurisdictions, but Tezuka Productions' trademarks on the name 'Astro Boy / Tetsuwan Atom' and on the character's visual design as a logo would survive any copyright lapse. Similar layering applies to almost every major franchise. The arrangement is one reason Japanese publishers and rights holders generally prefer to maintain registered trademarks aggressively even on inactive properties.