Rokumon Tengai Mon-Colle-Knight GB

The series features Mondo Ooya and his classmate/girlfriend Rockna Hiiragi (Rokuna in the Japanese version), whose scientist father Professor Ichiroubei Hiiragi invented a way to travel to Mon World (Roku Mon Sekai: the Six Gate World), where all sorts of magical creatures live. Together, they try to find six monster items which, when combined, could connect the Six Gate World with planet Earth for the better of both worlds. Rokuna and Mondo form the Mon Colle Knights and find out that when chanting a phrase-("With us, you can do it!") they can merge into monsters and control them into battle as well as aid with spells. Almost every episode, they battle Professor Hiiragi's rival Prince Eccentro (Count Collection in the Japanese version) and his two girl underlings Gluko and Batch (Goruko and Bachi in the Japanese version) who are after the same thing as the Mon Colle Knights, except that they intend to use the items to dominate both worlds.