Answer:
They all have a reading that is the same backwards.
思 SHI, omo(u) - think, believe
考 KOU, kanga(eru) - think, consider
落 RAKU, o(chiru), o(tosu) - fall, drop, lose
恵 KEI, E, megu(mu) - bestow a favour, bless
亜 A - rank, next, come after, Asia