Here we go:
Dil Pickles and Lisa Loud never really got on at times as they would clash in terms of clashing scientific ideas, Dil decided while trying to research something to remodel Lisa's revival chip and use it to revive Leni
A night after seeing Lenis grave, Dil snuck into the Loud house and went through the air vent to Lisa's room where despite all of the science stuff, it wasn't there, Dil then realised it must be in Kaoris room which he checked and found it, his sudden movements saw Kaori open her eyes, but Dils stealth allowed him to stay hidden which Kaori went back to sleep.
Afterwards Dil returned to his parents house and decided to see the tech in the Implant, it was insane, it was advanced technology that people weren't anticipating for another 20 years.
Dil created a second copy of the implant after a few nights and then he went to Lenis grave and used it, Leni was back, however she appeared weaker than usual, While the implant had worked, It had kept Lenis disease intact, but delayed its effects by a good few years.
"Hey Leni" said Dil
"Hi Dil, I knew you would come back to me" said Leni