Naruto is the type who'll go to any length for a friend.
Kyon from The Melancholy of Haruhi Suzumiya could also be appropriate. He returned from a world made specifically for him because the people there weren't the same ones he'd become friends with. He'd also make a great everyman character for your story while also coping well with the crossover element.
Sae Sawanoguchi from Magic User's Club.
Rushuna from Grenadier.
Otaru from Saber Marionette J.
Sasahara from Genshiken. That one'd be weird.
C-Ko from Project A-Ko.
Heck, Pinkie Pie may not be from an anime, but I doubt that would stop her from at least making a cameo.
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"Anyone can be a winner if their definition of victory is flexible enough." - The DM of the Rings XXXV
Kyon from The Melancholy of Haruhi Suzumiya could also be appropriate. He returned from a world made specifically for him because the people there weren't the same ones he'd become friends with. He'd also make a great everyman character for your story while also coping well with the crossover element.
Sae Sawanoguchi from Magic User's Club.
Rushuna from Grenadier.
Otaru from Saber Marionette J.
Sasahara from Genshiken. That one'd be weird.
C-Ko from Project A-Ko.
Heck, Pinkie Pie may not be from an anime, but I doubt that would stop her from at least making a cameo.
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"Anyone can be a winner if their definition of victory is flexible enough." - The DM of the Rings XXXV