Twitter was hiding this from me for several days. The comment called it Ruka with the kanji, which could be his sister, since he used kana when naming his other self. I never noticed before that Ruka is spelt with the name of a precious stone; it fits with other characters being codenamed with precious materials in a later volume.
>>3049807The chances of finding a waifufag whose interests and humour match yours is way too slim, you're better off finding someone who fits the other first and understands waifufaggotry second.