nyotaika-saiki-kusuo-ch37.png

Translation

• Context: characters see a girl appearing out of nowhere and are confused about where she came from. It's the protagonist, who has psychic powers, including the ability to turn into a girl.
• touzen, {boku ga nyotaika shita} ni kimatteru darou
  当然　僕が女体化したに決まってるだろう
  Obviously it's that {I turned into a girl}.
  Of course it's me turned into a girl.
• don
  ドン
  *sound effect used when something comes up suddenly.*
• Saiki Kusuo motoi Saiki Kusuko ga na
  斉木楠雄もとい斉木楠子がな
  Saiki Kusuo, or rather, Saiki Kusuko [did].
  • He, or rather, she is saying who nyotaika'd, since it's marked as subject by the ga が particle.
  • The name Kusuo ends in a kanji for "male," osu 雄, making it obviously a male name.
  • The name Kusuko ends in ko 子, which is a common suffix in female names, and typically used when coming up with a quick name for the girl version of someone.