| January | yukihiro officially joins the band |
| 28 | 8th single "winter fall" release *Oricon chart first appearance No.1 （Image song for TV Asahi Network drama "Chicago Hope 2"） |
| February | |
| 25 | 5th album "HEART" release *Oricon chart first appearance No.1 （"Shout at the Devil" Commercial image song for Daihatsu "move" -included in album "HEART") （"milky way" Theme song for TBS Network "Wonderful"-included in album "HEART"） |
| March | |
| 25 | 9th single "DIVE TO BLUE" release *Oricon chart first appearance No.1 （Commercial image song for "NTT Personal Kansai") （Ending theme song for TBS Network "Tokusou！Geinou Police kun"） |
| April | |
| 22 | Video "A PIECE OF REINCARNATION" release |
| May | |
| 01 | Nationwide Tour starts from Yokosuka Geijutsu Gekijo "L'Arc～en～Ciel'98 Heart ni hi wo tsukero！"(First Half) |
| 03 | Kyoto Kaikan Daiichi Hall |
| 05 | Kobe Kokusai Kaikan Harbor Land Plaza |
| 07 | Wakayama Shimin Kaikan（large） |
| 09 | Hikone Shimin Kaikan |
| 12 | Nagano-ken Kenmin Bunka Kaikan |
| 14 | Toyama Overd Hall |
| 15 | Kanazawa-shi Kanko Kaikan |
| 19 | Niigata Kenmin Kaikan |
| 21 | Tokuyama-shi Bunka Kaikan |
| 24 | Kurashiki Shimin Kaikan |
| 26 | Kagawa-ken Kenmin Hall |
| 28 | Tottori Kenritsu Kenmin Bunka Kaikan |
| 30 | Ichikawa-shi Bunka Kaikan |
| June | |
| 02 | Nagasaki-shi Kokaido |
| 04 | Kumamoto Shimin Kaikan |
| 05 | Kagoshima-ken Bunka Center |
| 12 | Fukushima-ken |
| 14 | Yamagata-ken Kenmin Kaikan |
| 16 | Akita Kenmin Kaikan |
| 17 | Gunma Kenmin Kaikan |
| 22 | Utsunomiya-shi Bunka Kaikan |
| 24 | Asahikawa Shimin Bunka Kaikan |
| 25 | Obihiro Shimin Bunka Hall |
| 27 | Kushiro Shimin Bunka Kaikan |
| 29 | Act City Hamamatsu（large） |
| July | |
| 01 | Kochi Kenmin Bunka Hall |
| 02 | Matsuyama Shimin Kaikan |
| 07 | Ibaraki Kenmin Bunka Center |
| 08 | Ohmiya Sonic City "HONEY" "Kasou" "Shinshoku-lose control-" First ever to release 3 singles at once *July 27th Oricon chart : #1"HONEY" #2"Shinshoku-lose control-"） （"HONEY" Theme song for TBS Network"Super Soccer"） （"HONEY" Commercial image song "NTT Personal Kansai"） （"Kasou" Ending theme for TV Asahi Network"Shinsou Kyumei! Uwasa no File"） （"Shinshoku-lose control-" Included in the original soundtrack"GODZILLA THE ALBUM" for movie"GODZILLA"） |
| 11 | Yokkaichi-shi Bunka Kaikan |
| 12 | Gifu Shimin Kaikan |
| 14 | Shizuoka Shimin Bunka Kaikan |
| 17 | Urawa-shi Bunka Center |
| 21 | Okinawa Convention Center |
| September | |
| 03 | Nationwide Tour "L'Arc～en～Ciel'98 Heart ni hi wo tsukero！" second half starts from Yokohama Arena |
| 04 | Yokohama Arena |
| 11 | Fukuoka Sunpalace Hall |
| 12 | Fukuoka Sunpalace Hall |
| 14 | Osakajo Hall |
| 15 | Osakajo Hall |
| 18 | Sendai Sunplaza Hall |
| 19 | Sendai Sunplaza Hall |
| 21 | Hokkaido Koseinenkin Kaikan |
| 22 | Hokkaido Koseinenkin Kaikan |
| 26 | Hiroshima Yubinchokin Hall |
| 27 | Hiroshima Yubinchokin Hall |
| 30 | Nagoya Rainbow Hall |
| October | |
| 01 | Nagoya Rainbow Hall |
| 05 | Nippon Budokan Starts airing Nippon Broadcasting System program "OH! DAIBA TO BLUE" （Every Monday-Friday 23:20-23:30 / program ends in December） |
| 06 | Nippon Budokan |
| 07 | 13th single "snow drop" release （Theme song for Fuji TV Network "Hashire!Police woman!"） |
| 14 | 14th single "forbidden lover" release （Theme song for Nihon TV Network "Shitterutsumori!?"） *October 26th Oricon chart : #1"forbidden lover" #2"snow drop" *Followed by July 26th Oricon chart, first in history for an artist to dominate #1 and #2 twice! |
| 15 | 1999 OFFICIAL CALENDER on sale |
| 17 | Osakajo Hall（Additional show） |
| 20 | Kokurirtsu Yoyogi Kyogijo Daiichi Taiikukan（Additional show） |
| 21 | Kokuritsu Yoyogi Kyogijo Daiichi Taiikukan（Additional show） （47 venues, 56 performances, 230,000 people / all tickets SOLD OUT in minutes!） |
| November | |
| 21 | Receive Yomiuri TV Network 31st Zennihon Yusenhousou Gold Request Grand Prix！ |
| December | |
| 04 | Trading card perfect collection on sale （117 kinds, including the "Limited Edition" <54 kinds> only sold at live concerts） |
| 23 | Live video "Heart ni hi wo tsukero!" release *#1 on Oricon video chart for 4 weeks in a row! （Sell over 350,000 units, which is exceptional for a music video!） |
| Latter half | L'Arc～en～Ciel Official Goods Collection First series on sale |
| 31 | Receive 40th THE JAPAN RECORD AWARD Excellency Award! （TBS Network） Perform at 49th NHK Kohaku Uta Gassen for the first time |
