 If you liked
Shinyaku Toaru Majutsu no Index
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 ...then you might like
Ore ga Heroine wo Tasukesugite Sekai ga Little Apocalypse!?
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Protagonist that continously get into problems as he keeps encountering girls that require saving. This grows a "harem" around him and as the girls tend to weild some sort of varying superpowers, thi coincidentally creates a powerful "faction" of sorts around the protagonist, powerful enough to influence the world conflicts. These novels also mix together fantasy and sci-fi elements frequently.