Thinking About Word-Level Pitch Accent: https://youtu.be/hWHvLvLs2KQ
NOTE: The pitch of "入（はい）る" is actually [-3'>, not [-2'>, due to a higher-level pitch-accent concept known as "特殊泊", or "special moras". "特殊泊" are "weak" moras that generally cannot become the accent-core of a word, and include ん, っ, the second half of extended vowels (such as the "あ" in "かあ"), and the second half of double-vowels (such as the "い" in かい). When the accent WOULD HAVE fallen on a "特殊泊", it gets bumped up to the previous mora instead. Because the second-to-last mora of "入る" is the second half of a double-vowel, its accent-core gets bumped up to "は". This doesn't have any influence on its conjugation; it still conjugates as a normal non-heiban verb. My bad for choosing a weird verb as an example.
