noun-modifying (irregular)
Internet slang used as a prenominal adjective to describe something or someone as overwhelmingly strong, powerful, or excellent. Often used in gaming, anime, and online communities.
このキャラはつよつよだから、初心者におすすめ。
This character is super strong, so I recommend it for beginners.
つよつよ装備を手に入れた。
I got some really powerful gear.
adverb taking the 'to' particle
exceedingly strong; perfectly fit
Archaic adverbial use, now obsolete. Describes something being extremely strong or perfectly fitting. Not used in modern Japanese.
古文では「つよつよと」のように使われた。
In classical Japanese, it was used as 'tsuyotsuyo to'.
Reduplication of 強い (つよい, 'strong') for emphasis. The exact origin is uncertain, but it likely emerged in online slang and gaming communities.