Lynn Okamoto, author of the Elfen Lied and Brynhildr in the Darkness manga, has recently tweeted an explanation as to why you will never see mobile phones in his works. He said he actively avoids drawing in objects that will date his work for future generations, and made an early decision not to put mobile phones into Elfen Lied, which became his first serialised work in Young Jump magazine in 2002.
Okamoto took this lesson from his experience of reading Mitsuru Adachi’s Miyuki manga, a series published in the ’80s which was one of his favourites when he was younger. He cites the appearance of a bank note which was no longer printed by the time Okamoto was reading, causing him to lose his sense of immersion in the story. From then on, he decided to avoid drawing anything that would connect his manga to a specific time period, saying that he wants his works to feel timeless to whomever may be reading, no matter when they were written. For this reason, he also refuses to draw home electronics and other such tech or equipment.