Love Hina: Ronin 15 is a one-of-a-kind weight gain visual novel based upon a fanfiction of a series originally written by Ken Akamatsu.

Motoko Aoyama, a young swordswoman/exorcist of the Shinmeiryu Swordschool, one day finds her once healthy lifestyle interrupted when a dueling injury leaves her housebound for several months. During this change of pace, she learns of the joys of food and gorging herself as a result of her boredom, as well as the effects of her new found fat on those around her, including her secret love interest. Her delightful days of watching her belly grow and the acceptance of her new flabby figure are interrupted, however, as a demonic presence once thought sealed away returns to take its revenge on the school and its residents, including Motoko's visiting roommates. It is now up to her to put her hunger pangs aside in favor of her sword and fight through her former friends in order to save a man she loves before the spirit can fatten her to immobility and beyond.

[From official site]