People are world jumping and then killing themselves.
In the original world, the 'I love you' male protagonist came from another world yet again with the explicit wish of spending time with his loved one, the female lead, and then he got killed the moment she finally realized that she loves him as per his/her spiritual mentor's contract.
And this comes full circle when our Female lead jumped to another world where she too could die by her mentor's contract after fulfilling her own wish of conveying her feelings to the male protagonist.