The following anime share the use of the semicolon as part of their names:
What is the reason for using the semicolon within the titles of these anime?
The best answer that I could make out myself for the use of the semi-colon in the names:
The semicolon in the names are used as a form of "pertaining to," however "not in possession of." Meaning--for example--"Steins" is related to "Gate" however, "Steins" is not in possession of "Gate." (This applies to the other two names as well.) We can see this because "Steins" does not make use of an apostrophe, which denotes possession.
We can see this by also rewording the titles of the anime:
Gate of Steins
Head of Chaos
Notes of Robotics
In this case, we see that "Steins," "Chaos," and "Robotics" all are related to the the preceding words in the reworded titles, just the same as if we made use of the semi-colon instead of, "of," in the original titles.
If lots of people start using a semicolon to connect words because they think it looks cool, then eventually it will become standard usage in World English and no one will complain
No need to speculate on "World English"; the series is Japanese, from a country simultaneously using four different official alphabets, and numerous languages in daily life. Japanese publishers feel very comfortable disregarding usual English grammar rules in their naming conventions. Note, even in Japanese, without translation, the series is still named "Steins;Gate". This disregard of usual English usage in titles has been true for many years now in Anime and Manga. It may be amusing to imagine the future response of "Users of Standard English", but totally unnecessary. For many years now, knowing native English speakers have shrugged, saying "It's from Japan!"