Here, you change KI, the syllable before MASU, to KU, and say KAKU. To get its TA-form, that is, the past or the perfective form, you change KI to I, and say KAITA (wrote, have/has written).
Pollard-Durodola, Sharolyn D. and Simmons, Deborah C. 2009. The Role of Explicit Instruction and Instructional Design in Promoting Phonemic Awareness Development and Transfer From Spanish to English.
In this case, Yeon Sang-ho chooses the character of Jeong Su-ni as his protagonist, which changes the entire initial perfective. However, as the season moves forward, the series starts to look a ...