On: New emperor, new era: How a single word defines Ja...

[masklinn]

> Oh, interesting, didn't know that they "create" a new Kanji with the sum of all the possible kanjis in the Era name.

They don't really, they create a new codepoint for a special (<square> in this case) composition of the era name.

> Should I be safe in the way that, even in my software doesn't support that unicode version, or my font doesn't have that symbol

It might fallback on the compatibility decomposition (the two combined kanji, so instead of "㍻" you'd have "平成".

[anoncake → masklinn]

It can fallback if the font does not have the new kanji, but not if the Unicode db is outdated.

[masklinn → anoncake]

Indeed, sorry for the confusing way I answered it.