Well, kanji is vital. In light novels, it can enhance the aesthetic appeal. Readers who are familiar with kanji can quickly grasp the intended meaning. Moreover, kanji is often used for names of characters, places, and important items in the story. Without kanji, it would be difficult to create unique and memorable names, and the overall feel of the light novel would be less distinct.
It really depends on the complexity of the light novel. Some simple ones might require you to know around 1,000 kanji, but for more complex ones, it could be 2,000 or more.
There are several. Kanji for directions like 東 (higashi, 'east'), 西 (nishi, 'west'), 南 (minami,'south') and 北 (kita, 'north') can be used when describing a place or a journey. Kanji for numbers are also common. For example, 一 (ichi, 'one'), 二 (ni, 'two') etc. Also, kanji for colors such as 赤 (aka,'red') and 青 (ao, 'blue') are often found in light novels to describe characters' appearances or the scenery.
No, it's not ethical. Kissing your girlfriend's sister is a betrayal of your girlfriend's trust and goes against the norms of loyalty in a relationship.
The 'My Little Sister Sagiri' light novel can be a great read for those who enjoy stories about family relationships. It may present a vivid portrayal of the siblings' dynamic. Maybe Sagiri is a shy or introverted character, and the story shows how the protagonist tries to understand and connect with her. The light novel might also use different literary devices to make the story more appealing, like detailed descriptions of the settings and the characters' emotions.
One main feature could be its character - driven plot. Since it's about a relationship with a sister, the characters' personalities play a big role. Another feature might be the exploration of family bonds. It may also have a unique art style if there are illustrations in the light novel, which can enhance the reading experience.