Same Sensei X Student forbidden relationship. Both really sweet and make you forget about their age gap.
Both are about "Contract Marriages". Both start off the relationship because of its mutual benefit. They eventually learn to Love as they face the trials and tribulations of doing life together. Nigeru wa Haji is more light hearted while HapiMari is more dramatic, but both have their really cute heartwarming and funny moments.
Rich arrogant guy who always gets his way vs. Headstrong stubborn common woman who stands up for herself. Both are good romantic stories and both have really handsome lead actors (RMPW - Shun Oguri and HapiMari- Dean Fujioka!!)