 If you liked
Strawberry Panic
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 ...then you might like
Assault Lily: Bouquet
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While these are completely different in terms of genre (Assault Lily involves action and Strawberry Panic centers around school life and romance), they have more similarities than it seems first. The protagonist is a transfer student entering girls' school where there is a whole lot of cuties fighting for her attention.
You will also be pleased if you like the 'mysterious senpai' trope.