Both are youthful highschool-setting dramas that show all different kinds of love and friendship. They are also both webseries available on YouTube

Both are set in the late 90s/early 2000s and the stories span over highschool, university and adulthood

Both Tokyo Live Story and Asunaro Hakusho are absolutely LEGENDARY 90s Japanese dramas and based on mangas by Saimon Fumi

Both of the dramas are based on mangas written by Saimon Fumi, and are iconic Japanese dramas from the 1990s

Both shows are based on mangas by Saimon Fumi, and are about university life, friendships and romantic relationships

I think the fact that they're both about the girl having a one-sided, long running love for the guy and the fact that they are primarily set when the characters are adults and working in hospitals definitely makes "Koi Tsuzu" have "They Kiss Again" vibes. Certain similar plot points which I won't reveal because *spoilers*

Although the type of story is different, both have a male/female power struggle as well as the fact that both "Hot Gimmick" And "5 to 9" are based on mangas written by the same author, Miki Aihara

Made by the same YouTube Channel, so they have similar vibes- it follows a group of young people and their different relationships.