From the top of my head I can recommend two books:
- All You Need Is Kill by Japanese author Hiroshi Sakurazaka. It's a light novel and there is also a manga adaption as well as the movie adaption Edge of Tomorrow which takes a lot of liberties with the material but it still entertaining. Even if you have already seen the movie I still recommend reading the novel. It's about an invasion of aliens that can only be fought with the use of a battle mech but even then only a single battle against them has only ever won. The book follows a grunt named Keiji Kiriya.
- Iron Widow by Canadian author Xiran Jay Zhao is a full length novel that is also about an alien invasion. A pair is always needed to take control of a Kaiju like creature the fight enemies. The book is very much inspired by Chinese history and you should definitely make the effort of googling all the character's names as soon as they appear. The book contains a bisexual love triangle so skip this book if such themes make you uncomfortable. The sequel Heavenly Tyrant is currently in the works and is supposed to be released in spring. Also follow the author on TikTok.