That Important Person is the one hundred and sixty-first chapter of To Love-Ru.
Rito watches as Lala and Haruna are trapped inside the monster. The monster then grabs Mikan, but Yami cuts her free. Yami then pushes Mikan out of the way, and gets attacked by the monster. Rito then musters up all of his strength and courage, and jumps straight into the monster. Rito then grabs both of them, and throws them out of the monster. Rito then realizes he has no strength left, but is glad that Haruna and Lala are safe. Nana then tells them all that if they hit the nucleus, that it will weaken the monster. Yami then transforms into a mermaid, and swims inside the monster. Yami finds the nucleus, and hits it with her transforming abilities. Meanwhile, Lala grabs her all purpose tool, and turns it into a sword, and cuts Rito free. Lala and Haruna then jump into the pool and they save Rito. Rito then thinks to himself about the times he has had with Lala. Rito then realizes that he loves her, realizing that when he sees her smile it makes him happy. But Rito also figures out that he loves Haruna. Meanwhile, Mikado-Sensei and the monster's own come to pick up the monster. Rito then looks at Lala and Haruna, and reiterates his feelings to himself.