Since I don't have much information about this 'Takamine - san' light novel with 'haite kudasai', here's a general tip for finding light novels. You can use search engines and type in keywords like 'Takamine - san light novel' and see what comes up. Also, consider following light novel reviewers on social media platforms as they might be aware of such works.
You can try looking for it on popular e - book platforms like Amazon Kindle or Barnes & Noble Nook. They usually have a wide selection of light novels.
Since I'm not familiar with that particular light novel, it's hard to give an exact similar one. However, if it's a slice - of - life or romantic light novel, you might like 'Toradora!'. It has a great story about relationships and character development. Another option could be 'Kaguya - sama: Love is War' which is also about the relationship between two main characters in a unique and comical way.
The secret in the pool was the Forbidden Door. According to the description in the original work and the drama version of " Celebrating Years," there was a forbidden door at the bottom of Taiping Courtyard's lake. It was a secret Ye Qingmei had left for Fan Xian. This forbidden door was related to Fan Xian's arrival in this world. It involved Fan Xian's incurable disease in his previous life and his spirit " passing through " Ye Qingmei's body when she was a child. The Forbidden Door could be a laboratory with modern high-tech equipment. However, the specific secret content was not mentioned in the search results provided.
Anliang's meaning was calm, comfortable, safe, and without danger, as well as happy, healthy, peaceful, quiet, auspicious, and happy. Good referred to good, outstanding, outstanding, virtuous, kind, gentle, and pleasant.
Liu Ruyu was a character in Maoni's novel, Celebrating Years. She was Fan Jian's concubine and Fan Sizhe's mother. To Fan Xian, she was the second concubine. At first, Liu Ruyu was hostile toward Fan Xian, worried that he would fight for the family property. However, as the plot developed, Liu Ruyu gradually understood Fan Xian's character and saw his actions of protecting his son in front of Fan Jian. The relationship between the two gradually reconciled and resolved their conflicts. In the end, Liu Ruyu's identity was also confirmed by Fan Jian, and she became the mother of the family. In the 2019 TV series of the same name, Liu Ruyu was played by Zhao Ke.