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Retina, 24 18 17 bytes

T`fkw`__y
\byy
He

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Explanation

T`fkw`__y

A simple character substitution (or transliteration): w expands to _0-9A-Za-z, and _ means "discard", so we remove f and k and then turn all other letters into y. By removing f and k we "normalise" the lengths of the words so that they now all have two more ys than they need.

\byy
He

This turns the first two y of every word into He, completing the transformation.

Retina, 24 18 17 16 bytes

1 byte saved based on an idea in MT0's answer.

\wf?k?
y
\byy
He

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Explanation

\wf?k?
y

This simply turns all letters into y, but if they are followed by an f or k we immediately replace that as well. By removing f and k we "normalise" the lengths of the words so that they now all have two more ys than they need.

\byy
He

This turns the first two y of every word into He, completing the transformation.

Retina, 24 18 17 bytes

T`fkw`__y
\byy
He

Try it online!

Explanation

T`fkw`__y

A simple character substitution (or transliteration): w expands to _0-9A-Za-z, and _ means "discard", so we remove f and k and then turn all other letters into y. By removing f and k we "normalise" the lengths of the words so that they now all have two more ys than they need.

\byy
He

This turns the first two y of every word into He, completing the transformation.

Retina, 24 18 17 bytes

T`fkw`__y
\byy
He

Try it online!

Explanation

T`fkw`__y

A simple character substitution (or transliteration): w expands to _0-9A-Za-z, and _ means "discard", so we remove f and k and then turn all other letters into y. By removing f and k we "normalise" the lengths of the words so that they now all have two more ys than they need.

\byy
He

This turns the first two y of every word into He, completing the transformation.

Retina, 24 18 bytes

T`l`y
Gy|[BW]yy
He

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Explanation

T`l`y

A simple character substitution (or transliteration): l expands to a-z, so we replace all lower case letters with y. However that gives a few more y than we need, depending on the word, so we have a second stage:

Gy|[BW]yy
He

This turns either Gy, Byy or Wyy into He, removing the extraneous ys and inserting the start of the Hey.

Retina, 24 18 17 bytes

T`fkw`__y
\byy
He

Try it online!

Explanation

T`fkw`__y

A simple character substitution (or transliteration): w expands to _0-9A-Za-z, and _ means "discard", so we remove f and k and then turn all other letters into y. By removing f and k we "normalise" the lengths of the words so that they now all have two more ys than they need.

\byy
He

This turns the first two y of every word into He, completing the transformation.