Tomoe could be a potential ally. He has a lot of knowledge about the spirit world and his loyalty to Nanami might extend to her sister as well. He could offer protection and advice when needed.
This is a highly improper and unacceptable act. It goes against social and legal standards. Any form of inappropriate contact within a family, especially of this nature, is strictly prohibited and can have serious consequences.
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.
One idea could be that Nanami's sister discovers a hidden power within herself that is different from Nanami's. Maybe she can communicate with a special type of spirit that no one else can. This could lead to her getting involved in some adventures that are parallel to Nanami's but also unique in their own way.
The recommendations for the humorous brother-sister romance are as follows:
1 "Di Ba"
Description: She is a young and promising lawyer who accidentally transmigrated to a different world. In this world, she met a genius emperor who was much older than her. The two fell in love at first sight, but the throne was an irreversible fact. Thus, she began a decade-long career of running around for the emperor, and he supported her all the way. The two gradually developed feelings for each other in their company, but they had to face the pressure of their families and power. In the end, they faced everything together and realized their dream of ruling the world.
2 My Sister
Description: Qin Zichuan is an ordinary university student who accidentally transmigrated to a different world one day and became the sister of Elf Prince Agnes, who was seven years younger than her. In this alternate world, Qin Zichuan began her unusual life, and her relationship with Agnes became closer and closer. However, when Qin Zichuan found out that she also had the Elven Prince's bloodline, she realized that she was also faced with an important choice. Between Agnes and the prince, she finally chose the latter and embarked on a journey to find true love with him.
Sister's Guardian
Su Xiaonuan is an innocent and kind girl, but she has an evil sister, Su Ye. Su Ye was a sinister and cunning demon. He had always tried to use his sister's power to achieve his goals. With the help of her younger brother, her sister fell into danger step by step. Hence, Su Xiaonuan decided to use her own actions to protect her sister from the evil torture. During this process, the relationship between the two gradually warmed up.
" Married with a Kiss " was a modern romance novel. It told the story of the protagonist who, by chance, got together with the male protagonist. After a series of misunderstandings and changes, she eventually became a famous fashion designer and returned to the male protagonist's side. The novel contained elements such as love, growth, and career change, which was very popular among readers.
While waiting for the anime, you can also click on the link below to read the classic original work of " Full-time Expert "!
I don't know who the author of the 'kiss kiss bang bang novel' is. There are so many novels out there and without more specific information, it's difficult to determine the author.