Kokoro Connect, ReLIFE Recommendations
Both series are a "deconstruction" (that is a very overused term.) of teenage social relationships. ReLIFE explores them from the point of view of a grown up dude who is shrinked into the body of a teenager and has to attend highschool, while Kokoro Connect makes its own entire cast go over and analyze their friendships because of some mysterious spell, bringing empathy and hostility between the group flourish.
Both are high school slice of life series involved romance and experiment elements.
Both of the characters are mentally grown up after overcoming the issue of jealousy, romance, misunderstandings and envy.
Both are romcom-esk about highschool students in a school setting. They revolve around somewhat sci-fi-ish plot devices, although in varying degrees. Relife has the medicine to set up the whole story, while kokoro connect has multiple of these incidents to encourage character interaction.
ReLIFE's characters are more obvious to read, and the character developments are all spelled out for you, while Kokoro Connect's are more subtle at times and may require some brains.
Kokoro Connect has more teenage melodrama than ReLIFE, but ReLIFE brings up more philosophical themes.
Overall, I recommend the manga for those who liked relife (start around chapter 109), and for those
explore relationships between people, how they deal with certain problems, etc
Both use highschool as a vehicle for an exploration of philosophy, with the main characters being monitored so that they will learn important lessons from the challenges they face. Both series have a very similar feel to them.
Both series shows a group of highschoolers during their time in high school. Protagonists experience weird things happening to their bodies and it changes their point of view and brings them closer together.