Well since I already mentioned it before, I personally believe that it comes down to Itsuki, Miku or Ichika, but with all the hints surrounding around Yotsuba, it's just a bit hard. Even Nino could be an option, though she's most likely not to be.
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It seems that also little Rena was Itsuki, at least from some words in chapter 80.
Still think about a quintuplet game at the time.
well the backside of chapter 84 confirms that Ichika was the Rena of the past.
^ Could be, or Fuutarou met more than one Lolikano in the past, in which case the "Rena" Fuutarou referred to (the one in the picture) could be anyone else.
i will support what @Self-Proclaimed King stated.. although it's just a possibility. a great twist tho
What if each tine he met Rena it was a different quintuplet? Just a theory tho
For disambiguation:
<=> SPOILER AHEAD <=>
> [Rena] refers to the present-day, disguised quint who met him at the lake (see "Chapter 42"). There is no "original" Rena, and the proper term to use would be [Young Nakano]. It's revealed that Rena is Itsuki.
> [Rena Nakano] refers to the quintuplets' mother.
> [Young Nakano], [Lolikano], or even [OG Rena] refers to the original Lolikano who: (1) first met Fuutarou in Kyoto (see "Chapter 34"); (2) presumably bought charms with Fuutarou (see "Chapter 34"); (3) took a picture with Fuutarou (?). [Lolikano] can be considered [The Girl in the Picture].
