The symbol after మి is the ma-ottu. It is the secondary form of మ. In Telugu, we write in syllables. First we write a primary letter (అక్షరం / aksharam), then we write the secondary vowel (గుణింతం / gunintam), then we write the secondary consonant (ఒట్టు /ottu). But, the reading order is different, the secondary consonant sound comes before the secondary vowel.
You can think of secondary consonants as similar to when we have two consonants in English. For example, in the word "summer". Imagine that we write the 2nd "m" under the first one, but write it a little smaller to save space on the page & to draw more focus to the first "m".