Japanese verbs are divided into three groups. Each group has its own patterns of conjugations. "Group 1" are the verbs that have the vowel I in the syllables before MASU. KAKIMASU (to write ...

Japanese dictionaries list verbs in this form ... there are two patterns for this conjugation. For one, you remove MASU, and add RU. For example, ORIMASU (to get off) becomes ORIRU.