There are often masters who play important roles. For example, Shirou Emiya can be one of the key characters in the Fate - related stories. He has his own goals and ideals which interact with Saber Alter's story.
The Super-Reflected Being was a key core card in the Explosive series, and also the most outstanding single card in the Harmonization system. It could be used anywhere from 6 to 9 stars. The Super-Reflectors could be used as synchronization materials. After leveling up, they could summon other powerful monsters at the same time, such as the Flame Paladin Emperor Charlie, the Gun Gun Fierce Dragon, or the Psy Skeleton King Omega. In some Dark Magic Decks, Super-Reflectors were also used to compress the deck so that the key cards were easier to use. Although the strength of the Super Reflectors in the game was very high, to use it, one needed to stuff some useless cards into the deck as a price. All in all, the Super-Reflected was a very powerful and common card, widely used in different card sets.
An alter ego is definitely a fictional character. It can be a way for an author or creator to explore different traits, emotions, or situations that the main character might not be able to express directly. It's a common literary device used to spice up the narrative.
Ultra Magnus is often portrayed as a strict and disciplined Autobot. He adheres to the rules and expects others to do the same. However, in some fanfictions, he also has a softer side that he shows to the reader. He might be protective of the reader, using his strength and strategic mind to keep them out of harm's way.
I'm not sure specifically as it could be a rather niche or new light novel. It might be about a character named Archid who experiences some sort of alteration in the story. Maybe it involves a fantasy world with magic and adventure where Archid's alteration plays a key role in the plot.
Alter Ego Visual Novel is often about exploring different personalities or alter egos within the story. It might involve characters dealing with their inner selves, making choices that reflect different aspects of who they could be, and usually has a strong narrative with various plot twists related to these concepts.
One common theme is redemption. Since Arjuna Alter is a darker version of Arjuna, many fanfics explore his journey towards redemption or at least a better understanding of himself. Another theme is his power and how it's different from the original Arjuna.
One popular alter history novel is 'The Man in the High Castle' by Philip K. Dick. It imagines a world where the Axis powers won World War II. Another is 'Fatherland' by Robert Harris, which is set in a world where Nazi Germany won the war. 'Jonathan Strange & Mr Norrell' by Susanna Clarke also has elements of alter history as it reimagines an England where magic exists in a different way than in our own history.